Geology Basics Page 1

Let’s start off with a review of the major rock classes.

There are three different types of rocks, Sedimentary, Igneous and Metamorphic. Any rock that exists can be classified in one of these three categories, which are dependent on how the rock formed.

SEDIMENTARY ROCKSedimentary rock is rock that was formed in a

one of two ways, thus there are two types of Sedimentary rock, clastic and non-clastic (or chemical).

Clastic Sedimentary rock is formed from bits and pieces of pre-existing rock that has been weathered (broken apart), eroded (transported away from its original location, usually by water or wind), and deposited. The loose deposits are then buried by other deposits, which compact the tiny grains together. The grains are then ‘cemented’ together to form new rock.

One of the common rock types in Arizona is Sandstone. Sandstone can be formed in the following process:

A mountain, composed of granite, is subjected to weather and wind, breaking apart the granite. One of the minerals in granite, quartz, is very resistant to weathering, and hangs around a long time. The tiny grains of quartz are eventually transported by either wind or water (or both) down a canyon to the valley below, which has begun to fill up with quartz grains. As more and more quartz grains pile on top of each other, compression begins to squeeze the grains together. The small gaps between the grains are filled with some cementing agent, like Calcite, which fuses the grains together into a layer of hard rock that stretches fromone end of the valley to the

other. Some Sandstone layers can be hundreds of feet thick and stretch for hundreds of miles.

Limestone is also a good example of sedimentary rock found throughout Northern Arizona, and can be formed as follows:

In Earth’s past, the sea level has been constantly changing. As the sea level rises, it travels inland, covering dry land. In a warm sea, there is an abundance of marine life, much of it microscopic. When these tiny organisms die, they deposit themselves on the ocean floor, along with terrestrial sediments and volcanic ash. Sediments are deposited at the bottom at the rate of a few inches every 100 years or so. The sea may retreat for a while, and return, adding to the sediment. If the sediment gets thick enough, it is compacted into rock. Because of the abundance of sea life, limestone usually has fossils embedded in it.

Shale is also found in Arizona. Shale is formed in the same way as Limestone, but the water where the sediments are deposited was lacking oxygen (such as in a swamp or lagoon, where the water doesn’t flow or move very much), and the ‘gook’ at the bottom is dark or black. The sediments are very small in size,

and squeeze into thin layers, one on top of the other.

Sedimentary rocks are arranged in layers called strata, and are generally laid down in level, horizontal layers. The Law of Superposition states that the layers at the bottom of a series of stratigraphic rocks were laid down first (and are older) than the layers on the top of the series. The Grand Canyon shows this very well. Rocks on the bottom of the canyon are much older than rocks at the top of canyon. As you descend down the canyon, the rocks get older and older.

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Here is a summary of sedimentary rocks you may see on this trip:

Rock Description OriginSandstone Grains of sand cemented together, usually by

Calcite. Color: tan, red (if iron is present), beige.Can form from buried sand dunes, or from a coastline or other near-shore environment.

Shale Grains of silt and clay (very fine particles) cemented together, usually breaking in flat, thin slabs. Can also be mudstone or siltstone.

Formed in a stagnant, oxygen-deprived marine environment, such as a swamp or lagoon.

Conglomerate Sand and pebbles deposited as gravel and then cemented together.

Forms in stream channels, and at the mouths of canyons and deltas.

Limestone Composed mostly of calcite deposited as a light-colored mud. Usually white or gray, often containing fossils.

Deposited in a marine environment, like a shallow inland sea with clear, warm water (tropical environment).

Sand stone can be formed in a near-shore environment (such as a beach or lagoon), as well as in arid environments (sand dunes). Sandstone is sand compacted and compressed, and cemented together. Anywhere that sand is collected can be a future source of sandstone. The example on the left is an example of ‘cross bedding’, where currents (wind or water) forms different layers of sand, each at different angles.

Shale is often found in fine layers (as in the pucture on left). Shales are formed in middle to deep ocean environments, and are composed of grains so small you need a microscope to see them.

Conglomerate (left) – Deposited in stream beds or delta areas, the rock is composed of rounded pieces of weathered rock due to water erosion.Breccia (right) – is similar to conglomerate except that the rock is composed of angular pieces of rock, suggesting non or little water erosion.

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IGNEOUS ROCKIgneous rock is ‘new rock’, formed from magma

or lava that cools. There are two types of igneous rock; Intrusive and Extrusive, which describes how the rock cooled off while solidifying. Intrusive Igneous rocks are cooled slowly beneath the surface of the Earth. The rocks surrounding the liquid magma act as an insulator, allowing the magma to cool very slowly (as much as thousands of years). Because the magma is cooling slowly, crystals have chance to grow. The slower the cooling process, the larger the crystals that form. Some quartz crystals in slow cooling magmas can be measured in feet. Later, these rocks can be exposed at the surface. Granite is the most common intrusive igneous rock (California’s Sierra Nevada Mountain Range is almost exclusively granite).

Extrusive igneous rocks are formed when underground magma comes to the surface and can form a volcano (magma becomes lava when it reaches the

surface). Because the temperature at the surface of the Earth is much cooler than the interior, the lava cools and solidifies very quickly (minutes to hours and sometimes days). The quicker it cools, the smaller the crystals that form. Obsidian is an extrusive igneous rock that cools so quickly, little or no crystals have a chance to form. In Northern Arizona, Basalt is very common. It is a dark, heavy rock, formed when very fluid lava flowed from a volcano along the ground. There are two types of lava flows, Pahoehoe which is formed from lava flowing quickly across the ground, and Aa, which is chunkier and does not flow as well.

Extrusive igneous rocks can also form when volcanoes emit ash and other pyroclastic material into the layer, where it settles, cools and hardens. Ryholite is a common type of rock formed this way. Chemically, Rhyolite and Granite are very similar, but Granite is cooled slowly, where Rhyolite is cooled quickly above ground.

Here is a summary of igneous rocks you may see on this trip:

Rock Class Description OriginBasalt Extrusive Igneous Very fine-grained black

rock, often showing small holes caused by gas bubbles while cooling.

Fluid lava from a volcano that flows along the earth’s surface.

Rhyolite Extrusive Igneous Light colored, very fine-grained rock. Sometimes has ‘flow lines’. Hard, breaks unevenly.

Non-fluid lava or ash from a volcanic eruption that deposits in fairly even layers.

Pumice Extrusive Igneous Usually red or gray, lightweight rock, full of holes. High air content allows rock to float in water.

Molten lava thrown into the air. Incorporates air when falling.

Granite Intrusive Igneous Common light colored rock with visible white and/or pink (feldspar), and clear (quartz) crystals that are interlocked. May also have black (biotite) crystals as well.

Cooled slowly underground in a magma chamber.

Monzonite/Diorite Intrusive Igneous Very similar to granite, but darker in color due to less quartz and feldspar and more biotite or hornblende.

Cooled slowly underground in a magma chamber.

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METAMORPHIC ROCKSMetamorphic Rocks are formed when pre-existing rocks are squished or heated, causing recrystallization of the

rocks to form different rocks. There are two common ways in which rocks can be metamorphosed. These are called contact metamorphism and regional metamorphism.

Contact metamorphism occurs in a small area, often when magma below the surface heats up the rock next to it, causing the contact rock to recrystalize. The heat needed for recrystallization can only travel a short distance, therefore the amount of rock changed is small in comparison to....

...regional metamorphism, where a large amount of rock is buried so deep below the surface that the pressure and heat is enough to cause recrystallization.

Some common metamorphic rocks are Marble, which is formed when Limestone is metamorphosed. Quartzite is formed when Sandstone or Conglomerate is recrystallized.

Other very common types of metamorphic rocks are gneiss (pronounced nice) and schist. These rocks are so altered that the parent rock is not easy to distinguish.

A summary of common metamorphic rocks:

Rock Description OriginMarble Light-colored rock composed

almost entirely of interlocking crystals. Visible calcite crystals are common.

Limestone that has been metamorphosed.

Quartzite Usually light-colored composed of recrystalized sand grains and pebbles.

Sandstone or Conglomerate that has been tightly compacted.

Greenstone Dark gray or green rock; massive (no visible crystals).

Created by the metamorphism of basalt or other dark igneous rock.

Gneiss Mostly dark rock with bands of lighter material running through it.

Most formed from the metamorphism of granite or sandstone.

Schist Very fine layered, dark rock. Weathered schist breaks along fine layers. Mica common.

Formed from very intense heat and pressure.

HISTORICAL GEOLOGYLet’s now go back to the Law of

Superposition. Remember that it states that in a series of sedimentary layers, the rocks at the bottom are older than the rocks at the top. Sedimentary rocks are also laid down in flat, horizontal layers. To the right is a cross section of some sedimentary rock layers. What layer is the oldest, A, B, C or D?

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The answer is A, because it is on the bottom. Let’s say later on, lava pushes itself up from below to reach the surface. It forms a dike(E), which is where the magma cooled. You now have igneous rock that runs through the sedimentary rock. In order for the igneous rock to form, it had to have cut through the sedimentary rock. So the igneous rock is younger than the sedimentary rock it cut through (duh?). In the diagram to the left, which letter represents the youngest rock?

The answer is E. Let’s continue. Sometimes, a series of horizontal sedimentary rock can be tilted (due to earthquake faults, or by squeezing of the rock layers). If you see sedimentary rocks that are tilted, you know that the rocks were formed first horizontally, and then the tilting occurred, because sedimentary rocks form horizontally. Possibly, after the tilting, more sedimentary rocks were deposited. In the diagram below, list the letters according to their age, from oldest to youngest.

Rock ‘A’ would be the oldest, followed by C. Those layers were then tilted, and layers ‘B’ and ‘D’ were deposited on top and are younger.

Faulting can also occur. This is when two blocks of the earth move past one another, either sideways or up and down. If a layer of sedimentary rock is offset, you know the faulting occurred after the rock was there (again, duh?). It is possible after the faulting that some new rock was deposited. In the diagram below, the order of events are listed from oldest to most recent:

1. Deposition of Layer A2. Deposition of Layer B3. Fault movement4. Deposition of Layer C5. Deposition of Layer D6. Intrusion of magma E

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HOW CAN YOU TELL HOW OLD ROCKS ARE?

There are a number of methods used to determine the age of rocks. In the above examples, a relative age was found, determining that certain rocks were older than others. However, this does not give us an absolute date (250 million years old, for example). To determine an absolute age of a rock, radiometric dating is used. There are certain radioactive elements that give off energy after they are formed. The amount of energy they release gradually decreases over time. The lower the energy released, the older the rock. Rates of decay of this energy have been calculated so that an approximate absolute age can be assigned to a rock.

Another way of determining the age of a

rock is by Radiocarbon dating, useful if the rock has fossils of once living creatures. All living creatures ingest Carbon while they are alive. After something dies, the Carbon is slowly decayed. By measuring the amount of Carbon that is left, geologists can approximate the age of something since it died.

Although absolute age is important, relative age is also important to geologists. There are fossils called index fossils, which are fossils of creatures who existed during a short time in Earth’s history. If you find an index fossil, you will immediately know the age of the rock. An example of an index fossil is a type of brachiopod (a mollusk type creature) similar to the picture below. Whenever you see this fossil, you know that the rock surrounding that fossil is about 330 million years old.

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GEOLOGIC TIMEGeologists don’t use an absolute time scale (so many millions of years old, etc.), but instead group the Earth’s

history in different stages depending on the climate and fossils found in each stage. The Earth’s history is broken up into four major eras; Pre-Cambrian, Paleozoic (Age of fishes), Mesozoic (age of Reptiles) and Cenozoic (age of mammals). Each era is broken up into periods. See the table that follows for reference.

Geologic Time ScaleEra Period

Years ago (Millions)

General Characteristics

Arizona Characteristics

Quaternary 1.8-present Ice agesSan Francisco Peaks, Sunset Crater, Lava River

Cave form by volcanism

CenozoicTertiary 65-1.8 Andes, Himalayas, Alps

form.

Northern Arizona rises (24 m.y.a.), Basalt volcanism common (8 m.y.a.)

Colorado River begins cutting Grand Canyon (3 m.y.a.)

Cretaceous 136-65

Flowering plants appear; Mass extinctions of many

species including dinosaurs, other land

species.

Seas invade briefly. Thick sediments of Coalmine Canyon were deposited, along with some cola

deposits.

Jurassic 190-136

Rocky Mountains rise, volcanoes of Western

U.S. become active; first birds, largest dinosaurs

thrive.

Thick sandstone deposits. Kayenta Formation (where dono tracks are located) were formed

during this period.

Mesozoic

Triassic 225-190First dinosaurs appear, first mammals, modern

insects.Dune deposits (sandstone) in north.

Permian 280-225

Ferns, fish, amphibians and reptiles flourish,

mass extinctions of many sea-living invertebrates.

Sand dunes form in north. Top four layers of Grand Canyon rock (Kaibab Limestone,

Toroweap Formation, Coconino Sandstone, Hermit Shale) are deposited in alternating shallow

sea/shoreline environments.

Carboniferous(Pennsylvanian

and Mississippian)

345-280

Ice covers highlands, swamps cover lowlands;

coal forming swamps/forests

In Pennsylvanian, large limestone deposits with numerous fossils from a marine environment.

In Mississippian, sandstone deposits in Northern Arizona. Grand Canyon layers deposited are

Redwall limestone and the Supai group.

Devonian 395-345 First forests, amphibians, insects

Most Devonian rocks eroded. Rocks that exist are marine deposits.

Silurian 430-395 Land plants appear Silurian rocks eroded. No record.

Ordovician 500-430Many volcanoes and

mountains form; North America flooded.

Brief marine invasion

Paleozoic

Cambrian 570-500Shallow seas cover continents; trilobites, brachiopods common

Sea advances from West, depositing sandstone, shale and limestone. At Grand Canyon, Muav Limestone, Bright Angel Shale and Tapeats

Sandstone are deposited.

Precambrian --- 4,600-570Some mountains begin to

form, oxygen in atmosphere increases

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FOSSILSIn order for organsims to become fossilized, the organism must be buried quickly after its death by sediments.

Quick burial prevents dead organisms from being eaten by animals, and slows the decay process. Plants or animals that lived in or near water are much more commonly preserved as fossils as are organisms on land.

Besides the actual body parts of plants and animals, living creatures can also leave behind trace fossils. Trace fossils show the evidence of a living creature. Trace fossils can include footprints, worm burrows, or even animal poop.

Below is alist of possible fossils we may see during our hike into the Grand Canyon. Name of Fossil Sketch CommentsCrinoid (Sea lily) Can be regarded as an

inverted starfish with a stalk or stem attached to the underside. The stem parts are very common

as fossils.

Bryozoan (moss animal) Bryozoans include a large group of animals that grow in colonies, and

appear moss-like to the naked eye. These

animals had a complete degestive tract, and were

abundant in the Paleozoic.

Coral Kaibab Limestone

Derbyia (Brachiopod) In Paleozoic rocks, the most abundant fossils are brachiopods (‘bracks’

for short).

Meekella (Brachiopod) At first site, brachiopods look like a clam shell. On closer inspection, you will notice that a brachiopod is symmetrical (if you laid it down flat and cut it in

half, the two halves would be identical.

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VOLCANOES

A volcano is a mound, hill or mountain constructed by solid fragments, lava flows, and or dome-like extrusions deposited around a vent from which the material is extruded.

The form of a volcano is determined by the composition of the erupting magma and the type of erupted products. Their shapes are determined to a large degree by the explosivity of the eruptions, and to the abundance of water and its degree of interaction withmagma.

There are three main types of volcanoes; Cinder cones, Composite Cones and Shield Volcanoes. They are each described below.

CINDER CONESCinder cones (like Sunset Crater) are the simplest

type of volcano. They are built from particles and blobsof lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. Cinder cones are numerous in western North America as well as throughout other volcanic terrains of the world.

COMPOSITE VOLCANOESSome of the Earth's grandest mountains are

composite volcanoes -- sometimes called

stratovolcanoes. They are typically steep-sided, symmetrical cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet above their bases. San Francisco Peak just north of Flagstaff is a composite volcano.

Most composite volcanoes have a crater at the summit which contains a central vent or a clustered group of vents. Lavas either flow through breaks in the crater wall or issue from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dikes that act as ribs which greatly strengthen the cone.

The essential feature of a composite volcano is a conduit system through which magma from a reservoir deep in the Earth's crust rises to the surface. The volcano is built up by the accumulation of material erupted through the conduit and increases in size as lava, cinders, ash, etc., are added to its slopes.

When a composite volcano becomes dormant, erosion begins to destroy the cone. As the cone is stripped away, the hardened magma filling the conduit (the volcanic plug) and fissures (the dikes) becomes exposed, and it too is slowly reduced by erosion. Finally, all that remains is the plug and dike complex projecting above the land surface -- a telltale remnant of the vanished volcano. can flow great distances from the active vents. Although Hawaiian-type eruptions may destroy property, they rarely cause death or injury.

SHIELD VOLCANOESShield volcanoes are built almost entirely of fluid lava

flows. Flow after flow pours out in all directions from a central summit vent, or group of vents, building a broad, gently sloping cone of flat, domical shape, with a profile much like that a a warrior's shield. They are built up slowly by the accretion of thousands of flows of highly fluid basaltic (from basalt, a hard, dense dark volcanic rock) lava that spread widely over great distances, and then cool as thin, gently dipping sheets. Lavas also commonly erupt from vents along fractures (rift zones) that develop on the flanks of the cone. Some of the largest volcanoes in the world are shield volcanoes.

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MAGMA & LAVAIf magmas cool rapidly, as might be expected near

or on the Earth's surface, they solidify to form igneous rocks that are finely crystalline or glassy with few crystals. If magmas never reach the surface to erupt and remain deep underground, they cool much more slowly and thus allow ample time to sustain crystal formation.

Lava is red hot when it pours or blasts out of a vent but soon changes to dark red, gray, or black as it cools and solidifies. Very hot, gas-rich lava containing abundant iron and magnesium is fluid and flows like hot tar, whereas cooler, gas-poor lava high in silicon, sodium, and potassium flows sluggishly, in pasty, blocky masses.

TYPES OF LAVA FLOWSPahoehoe, Aa: Lava flows form more that 99

percent of the above-sea parts of Hawaiian volcanoes. Pahoehoe (pronounced "pah-hoy-hoy") and aa (pronounced "ah-ah") are the two main types of Hawaiian lava flows, and these two Hawaiian names, introduced into the scientific literature in the late 19th century, are now used by volcanologists worldwide to describe similar lava-flow types. Pahoehoe is lava that in solidified form is characterized by a smooth, billowy, or ropy surface, while aa is lava that has a rough, jagged, spiny, and generally clinkery surface.

Hawaiian lava is fluid enough to travel great distances, especially if it is transported through lava tubes. Some historic flows are longer than 30 miles; in general, pahoehoe flows tend to be longer than aa. Both aa and pahoehoe solidify into black, dense rock called basalt. Basalt is formed when magma extrudes onto the Earth’s surface and cools rapidly.

The Grand Canyon Page 1The Grand Canyon is one the world’s finest displays of a large amount of sedimentary rock. The rock layers

are exposed because of the cutting action of the Colorado River, which has cut a canyon over a mile deep through layers of rock. By studying the exposed rock, geologists can determine the type of setting and climate of the Earth during the time each rock layer was forming.

For additonal help on Sedimentary rocks and how they are formed, read the Geologic Basics handout.The stratigraphic chart above is a representation of the rock layers found in the Grand Canyon. Included in the

chart is the age and thickness of each layer. You can use this chart to help you draw your own stratigraphic chart (Assignment #5).

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•Kaibab Limestone - This layer averages about 250 million years old and forms the surface of the Kaibab and Coconino Plateaus. It is composed primarily of a sandy limestone with a layer of sandstone below it. In some places sandstone and shale also

exists as its upper layer. The color ranges from cream to a greyish-white. When viewed from the rim this layer resembles a bathtub ring and is commonly referred to as the Canyon's bathtub ring. Fossils that can be found in this layer are brachiopods, coral, mollusks, sea lilies, worms and fish teeth.

•Toroweap Formation - This layer averages about 255 million years old and is composed of pretty much the same

material as the Kaibab Limestone above. It is darker in color, ranging from yellow to grey, and contains a similar fossil history.

•Coconino Sandstone - This layer averages about 260 million years old and is composed of pure quartz sand, which are basically petrified sand dunes. Wedge-shaped cross bedding can be seen where traverse-type dunes have been petrified. The color of this layer ranges from white to cream colored. No skeletal fossils have yet

to be found but numerous invertebrate tracks and fossilized burrows do exist.

•Hermit Shale - This layer averages about 265 million years old and is composed of soft, easily eroded shales which have formed a slope. As the shales erode they undermine the sandstone and limestone layers above which causes huge blocks to fall off and into the lower reaches of the Canyon. Many of these blocks end up in the side drainages and down on the Tonto Platform. The color of this layer is a deep, rust-colored red. Fossils to be found in this layer consist of ferns, conifers and other plants, as well as some fossilized tracks of reptiles and amphibians.

•Supai Formation - This layer averages about 285 million years old and is composed primarily of shale that is intermixed with some small amounts of limestone and capped by sandstone. The limestone features become more and more prominent in the western regions of the Canyon, leading one to believe that that region was more marine. The eastern portions where probably a muddy river delta that fed into an ancient sea. The color of this layer varies from red for the shale to tan for the sandstone caps. Numerous fossils of amphibians, reptiles and terrestial plants exist in the eastern portion which are replaced by marine fossils as you move westward.

•Redwall Limestone - This layer averages about 335 million years old and is composed of marine limestones and dolomites. This is probably the most prominent rock layer in the Canyon as it usually forms a sheer cliff ranging from 400-500 feet in height, which has become a natural barrier between the upper and lower regions of the Canyon. The only way though this barrier is in areas where the rock has faulted and broken apart to form a slope which can be climbed upon. The deep reddish color of this layer is caused by iron oxides leaching out of the layers above it and staining its outward face. Behind the reddish face the rock is a dark brownish color. Numerous marine fossils can be found in the Redwall Limestone including brachiopods, clams, snails, corals, fish and trilobites. Many caves and arches can also be seen in the Redwall.

•Muav Limestone - This layer averages about 515 million years old and is composed primarily of limestone

that is separated by beds of sandstone and shale. The Mauv Limestone layer is much thicker in the western areas of the Canyon than it is in the east. Its color is grey and it does not have much in the way of fossils, some trilobites and brachiopods.

The Grand Canyon Page 3• Bright Angel Shale - This layer averages about 530 million years old and is composed primarily of

mudstone shale. It is also interbedded with small sections of sandstone and sandy limestone. The retreat of the Canyon rim is attributed primarily to the erosion of this layer which forms the top of the Tonto Platform. The plateau is much wider in the eastern portions of the Canyon where the Bright Angel Shale contains less sand and is more easily eroded. The color of this layer varies with its compostion but it is mostly various shades of green with some grey, brown and tan thrown in here and there. Fossils to be found in this layer consist of marine animals such as trilobites and brachiopods. • Tapeats Sandstone - This layer averages about 545 million years old and is composed of medium-grained and coarse-grained sandstone. Ripple marks formed by ocean waves of an early Cambrian sea are common in the upper layer. The Tapeats is similar to the Redwall in that it forms a barrier between upper and lower reaches of the Canyon that can only be traversed where a fault has caused its collapse. The color of this layer is dark brown and it contains fossils of trilobites. brachiopods, and trilobite trails.

The following mnemonic sentence provides an easy way to remember the primary rock layers in the Grand Canyon: Know (Kaibab Limestone) The (Toroweap Formation) Canyon's (Coconino Sandstone) History (Hermit Shale), Study (Supai Formation) Rocks (Redwall Limestone) Made (Muav Limestone) By (Bright Angel Shale) Time (Tapeats Sandstone).

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Where did all of the rock come from?Geologists have this question pretty much

wrapped up, aside from some missing layers, or unconformities, that have been completely eroded away. Again there were a number of forces at work and this is where continental drift, vulcanism and climatic change come into play.

The fact that the Earth's continents are not fixed in place but rather float on a sea of molten rock, means that they move around quite a bit, relatively speaking. The surface of the Earth is composed of about twenty of these "plates" which form its crust. Seven of these plates are very large and consist of entire continents or sea floors and the rest are smaller in comparison. The plates are average out to be about 50 miles or 80 kilometers thick and float on top of the Earth's mantle. The plate which contains the Grand Canyon, the North American plate, was at one time considerably further south than its present location and therefore had a much different climate. In time it has gradually moved north and rotated about ninety degrees to its present location and configuration.

The conflict between the plates is also frequently responsible for mountain building activity. As the plates are forced together they sometimes buckle which causes mountain ranges to be formed along the contact point. This is how the Rocky Mountains, the Sierra Nevada and the costal mountains of California were formed and how the Aleutian Island are being formed today. A much older range of mountains, which geologists suspect were much higher than todays Rocky Mountains and may even have rivaled the Himalayas, now forms the base of the Grand Canyon. The rocks that made up these mountains are about 1.7 billion years old, or about one-third the age of our planet. These mountains have long since eroded away and sedimentary deposits have covered them over.

The sediments that covered the roots of these ancient mountains were deposited by a series of advancing and retreating ocean coast lines. As the climate of our planet warms and cools the median sea level of the planet rises and falls due to the melting and freezing of the polar caps. When the sea level rises, land areas which are close to the coast and relatively low in altitude are sometimes submerged. This was the case with the land area of the Grand Canyon and is why so many different sedimentary rock layers exist. Each of these was formed by a different period in which the ocean moved in and covered the land, stayed for a while, and then retreated again. Limestone deposits are created when the ocean moves in and slates, shales and mudstone deposits are created when the ocean moves out and the area is covered by silts washing into the retreating ocean.

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How do we know this? Well, the fact is that most of the rock in the Grand Canyon is composed of sedimentary rock which can only be

formed at the bottom of the ocean or in shallow coastal plains. The Kaibab Limestone which is the current top of the Grand Canyon is composed mostly of a sandy limestone, with some sandstone and shale thrown in for good measure. This means that it was probably formed in a shallow sea near the coast. The fact that it contains fossils of creatures that used to live in the ocean, like brachiopods, coral, mollusks, sea lilies, worms and fish teeth, only tends to reinforce this belief. The intrusion of sandstone and shales into this later means that at times the layer was also above the surface of the water but still very close to the edge. Sandstones are solidified sand which are typically fields of sand dunes or beaches, and shales are solidified mud which are common to river deltas. By dating the fossils found in the rock of the Kaibab Limestone, geologists have determined that it is approximately 250 million years old, and this is the youngest layer.

So where are the younger rocks? The younger rocks have already been eroded away by the forces of nature, at least in the immediate vicinity of

the Grand Canyon. Some of the younger layers, like the Navajo Sandstone of which the Vermilion Cliffs and the rock of Zion National Park are composed, can be found in the region north of the Grand Canyon. Going even further north results in even younger rocks as can be seen in Bryce Canyon. The area from Bryce Canyon down to Grand Canyon is typically referred to as the Grand Staircase.

Lava Tubes & Lava River Cave Page 1

THE ROLE OF LAVA TUBES In the western U.S. there are two principal types of caves: solution caves in limestone and lava tube caves in basalt. Their origins could hardly be more different. Limestone caves are cavities slowly dissolved by acidic groundwater in bedrock laid down millions of years previously. Lava tube caves are cavities once occupied by flowing lava, in bedrock emplaced by and usually no older than the lava tube itself. Lava tubes are conduits on or within a lava flow that carry lava to the advancing front of the flow. They form only in pahoehoe lava (pronounced pah hoy hoy), a highly fluid type that behaves much like water as long as it stays hot. However, it quickly cools and hardens when exposed to the atmosphere, becoming a strong and durable rock known as basalt. Simply stated, tubes form initially by hardening of the outer surfaces of masses of lava, inside which the fluid lava continues to move. Because basalt is a good insulator, lava can travel great distances inside lava tubes, with only slight loss of heat. (Heat loss of about 3 degrees F. per mile has been measured in a Hawaiian lava tube.) That is why lava tubes are a principal means by which pahoehoe lava is spread thinly over wide areas. HOW LAVA TUBES FORM Lava tubes originate in two distinctly different ways: as surface tubes, or by roofing of a lava channel. Surface tubes form all at once, on an existing surface (hence the name). Roofing is an evolutionary process that forms a roof over an existing channel.

LAVA TUBES Nearly all lava tubes (other than surface tubes) begin with formation of a roof over a river of lava flowing in an established lava channel. Steady eruption of pahoehoe lava will inevitably result in formation of channels, because eventually there simply isn't enough lava to supply all parts of the growing lava field. Outer parts of the spreading lava field stagnate, harden, offer resistance, and lava flows where resistance is least. (The route of a channel may be controlled by pre-existing topography.)

Lava rivers, like rivers of water, can meander, overflow their banks, build levees, erode their channel downward and, of primary importance to the formation of lava tubes, can "freeze over," or develop a roof. Unlike rivers of water, lava rivers are larger nearer the source. If lava flow in a channel is moderate and steady, crusts build from each side of the channel to meet in the center, forming a roof, and a lava tube is born. Roofs are often broken and swept away by surges in the lava river. They may reform, or the pieces may drift along to a bend in the channel where they jam together, forming another roof. If a roof lasts long enough, it is further thickened and strengthened as lava congeals on its underside, or overflows adding to its top side. Once a roof is formed, the resultant tube becomes, in effect, an extension of the vent, through which lava can pass with very little loss of heat. What happens next depends on the duration and especially the regularity of lava flow. Irregular flow causes blockages and overflows, and creates short-lived lava tubes. Long lava tubes require eruptions of steady rate and long duration.

Lava Tubes & Lava River Cave Page 2 LAVA RIVER CAVE Lava River Cave probably formed within a few hours after a brief volcanic eruption. In comparison to other geologic events, like the cutting of a canyon or the movement of a glacier, Lava River Cave formed in the briefest of moments. Since the cave appears today much as it did shortly after its formation, it is indeed a "frozen moment" in geologic time. Lava River Cave is a unique kind of cave known as a "lava tube." It is the longest cave of this kind in Arizona. Geologists believe Lava River Cave was formed sometime between 650,000 and 700,000 years ago when molten lava erupted from a volcano near the present day site of Michelbach Ranch. When the lava came to the surface its temperature was hotter than 2,000' F! Lava Flow Features Lava River Cave contains a variety of outstanding lava flow features. These features also used to exist outside the cave, but have long since been washed away by wind and rain, and overgrown by plants. The lava flow features in this cave include flow ripples, splashdowns, cooling cracks and lavasicles.

Flow ripples can be observed on most of the floor throughout the last two thirds of the cave. This gives the floor the appearance of a frozen river. Actually the floor is a "frozen river" of lava which flowed through the cave shortly after the walls and ceiling hardened.

Splashdowns appear to be rocks floating on the frozen river because they actually were. Shortly after the ceiling hardened a few rocks fell

into the still flowing floor and floated downstream a little ways before the floor also hardened. Cooling cracks are long cracks in the floor ceiling and walls. Some of these are six inches wide, three

feet deep and over twenty feet long. These cracks formed as the lava cooled and hardened because lava shrinks when it cools.

Lavasicles are very small icicle-like formations which formed after the walls and ceiling hardened. For some reason a hot blast of gas shot through the tube shortly after it formed and partially remelted the walls and ceiling. This caused drips of remelted lava to form and quickly hardened into lavasicles. Nature's Ice Box Lava River Cave is an amazingly simple natural ice box. In fact, it could be considered the largest "refrigerator" in northern Arizona. On the hottest day of summer, when the temperature outside the cave is over 90 F, just inside the temperature is 35'F and sometimes there is ice! There are two reasons that temperatures within the cave remain so cold: 1. The lava rock which formed the cave is an excellent insulator. Its dark color and very dense composition prevent heat from traveling

Lava Tubes & Lava River Cave Page 3 from the surface into the cave. 2. Lava River Cave is cold because of its general shape. The highest point of the cave is the entrance. Since hot air rises and cold air falls, cold air falls into the cave during winter and is trapped there throughout the summer. Creatures That Like The Cold And Dark Lava River Cave is occasionally used by animals and insects. These include crickets, beetles, porcupines, squirrels and bats. All of these creatures are shy, and since so many people visit Lava River Cave, it is rare to actually see them while in the cave. We do know that animals use the cave because their droppings can be observed beneath rocks and along the walls. Animal droppings are probably not a wonderful lunch-time topic, but for the complete Lave River Cave experience, you might want to see if you can find and identify these three types during your visit: A Few Words About Bats Bats are truly amazing little creatures which unfortunately have an undeserved bad reputation. A lot of people think bats are filthy, disease-ridden, flying mice. This is not the case. Bats are actually very clean and no more likely to contract rabies than your household pet. They are very important to the environment since they are the only major night-flying predator of insects. In one night some individual bats can nearly eat their own weight in insects! Anyone who has had their share of mosquito bites ought to appreciate that. Bats and other creatures which like to live in cold, dark caves are very vulnerable to human disturbance. Please remember to treat any creatures you observe within Lava River Cave with respect and give them lots of room. NOTES ABOUT HIKING IN THE CAVE:

1. Watch for ice near the entrance. Once inside the cave, the rocks near the entrance are covered with ice most of the year. Please go slow and be careful not to slip!

2. Wear long pants! The basalt is jagged and can easily scrape you if you brush against it. Also, the temperature in the cave is around 35 degrees, and we may be in there for an hour or more, which leads us to…

3. Bring a warm sweatshirt or jacket! It will be cold in the cave.

4. Watch your head!!! Because there is no lighting in the cave, it is easy to lose track of the height of the roof. Use your flashlight to illuminate the roof as well as the floor. Which brings us to…

5. Bring a flashlight!!!

Red Mountain Page 1

Information and images from http://wrgis.wr.usgs.gov/fact-sheet/fs024-02/

Red Mountain, located in the Coconino National Forest of northern Arizona, 25 miles northwest of Flagstaff, is a volcanic cinder cone that rises 1,000 feet above the surrounding landscape. It is unusual in having the shape of a "U," open to the west, and in lacking the symmetrical shape of most cinder cones. In addition, a large natural amphitheater cuts into the cone's northeast flank. Erosional pillars called "hoodoos" decorate the amphitheater, and many dark mineral crystals erode out of its walls. Studies by U.S. Geological Survey (USGS) and Northern Arizona University scientists suggest that Red Mountain formed in eruptions about 740,000 years ago.

Red Mountain is unusual in that its internal structure is exposed. This is not the case at most cinder cones in the San Francisco Volcanic Field, because erosion has not had

enough time to expose their internal features. Although human quarrying creates frequently changing glimpses into a few of the cones in the volcanic field, quarries generally are unsafe for tourists and public access commonly is denied.

An "ideal" cinder cone forms when eruption occurs on flat ground. From deep within the Earth, magma charged with gas (like a carbonated drink) rises through a vertical pipe-shaped conduit and erupts as a fountain of frothy lava that may spray as high as 2,000 feet into the air.

As an individual blob of this frothy molten rock flies through the air, it cools quickly enough to solidify before falling back to Earth. Many gas bubbles remain trapped in the fragments. If small, these fragments of rock are called "cinders," and if larger, "bombs." As eruption continues, cinders accumulate to form a conical hill. Periodically, the flanks of the growing hill

may become so steep that lobes and sheets of cinders slide downward. When lava fountaining ends, a symmetrical cone-shaped bill, commonly indented by a summit crater, has been added to the landscape. Internally, the cone is a pile of loose cinders in layers that dip away from the volcano's vent in all directions.

Red Mountain Page 2

Information and images from http://wrgis.wr.usgs.gov/fact-sheet/fs024-02/

During the waning stage of an ideal cinder-cone eruption, the magma has lost most of its gas content. This gas-depleted magma does not fountain but oozes quietly into the crater or beneath the base of the cone as lava. Because it contains so few gas bubbles, the molten lava is denser than the bubble-rich cinders. Thus, it burrows out along the bottom of the cinder cone, lifting the less-dense cinders like a cork on water, and advances outward, creating a lava flow around the cone's base. When the eruption ends, a symmetrical cone of cinders sits at the center of a surrounding pad of lava.

Field studies conducted by U.S. Geological Survey (USGS) and Northern Arizona University scientists suggest that Red Mountain grew on a nearly flat surface that may have sloped gently to the north. However, little else about this volcano mimics the features of an ideal cinder cone. When viewed from above, Red Mountain is a U-shaped landform open to the west, rather than a symmetrical cone. The base of the U is a curving ridge that forms the highest part of the mountain. The nearly half-mile-long arms of the U slope down to the west and merge with the gently rolling surface of the Red Mountain lava flow.

By carefully measuring the orientation of cinder layers over all parts of Red Mountain, geologists have mapped a radial pattern of layers, dipping away from the middle of the U in all directions. At the amphitheater, all the exposed layers dip uniformly to the northeast. This pattern indicates that the vent is somewhere in the middle of the U and not at the amphitheater.

The shape of Red Mountain and its overall pattern of cinder layers raises the question of why a symmetrical cone was not created around the vent at the center of the U. Three possible explanations are:

• If the lava-fountaining phase of eruption occurred during a time of sustained wind blowing from west to east, most cinders could have been blown eastward creating the asymmetrical shape of Red Mountain. However, eruptions of the type. that built Red Mountain usually last several years to a decade or longer, and it seems unlikely that a westerly wind could have persisted for such a period of time.

• Perhaps the conduit through which magma rose to the surface was inclined eastward enough to give the same effect as a westerly wind, but this seems unlikely because the driving force for rising magma is the buoyancy of

Red Mountain Page 3

Information and images from http://wrgis.wr.usgs.gov/fact-sheet/fs024-02/

very hot volcanic gases. Like a cork released in water, such gases tend to rise vertically rather than follow an inclined path.

• The most likely possibility is that the waning-stage lava flow of the Red Mountain eruption rafted the western section of the cinder cone away, like wood on flowing water. When gas-poor molten lava burrows its way outward beneath a cinder cone, it may either leave the cone undisturbed or carry pieces piggyback, literally floating pieces on the surface of the denser lava. Many examples of both situations are known worldwide; a spectacular example of rafting is found at Sunset Crater National Monument, northeast of Flagstaff. At Red Mountain, geologists have discovered several outcrops of layered cinder deposits, some of which are hundreds of feet wide and tens of feet thick, at the top of the lava flow. Typically, these "floaters" form hills on the surface of an otherwise fairly flat flow. Apparently, molten lava oozed out beneath the west base of Red Mountain and rafted away much of that side of the cinder cone, creating its U shape.

Meteor Crater Page 1

The Barringer Meteorite Crater (also known as "Meteor Crater") is a gigantic hole in the middle of the arid sandstone of the Arizona desert. A rim of smashed and jumbled boulders, some of them the size of small houses, rises 150 feet above the level of the surrounding plain. The crater itself is nearly a mile wide, and 570 feet deep. When Europeans first discovered the crater, the plain around it was covered with chunks of meteoritic iron - over 30 tons of it, scattered over an area 8 to 10 miles in diameter.

Although meteorite falls had been reported for thousands of years, until this century no one had ever identified a crater created by such a fall. Even a meteorite as large as the 66-ton Hoba, the largest ever discovered, may be slowed so much by the Earth's atmosphere that it lands without making a significant hole. In 1891 Grove Karl Gilbert, then chief geologist for the U.S. Geological Survey, decided to test two conflicting hypotheses about the crater. The first was that the crater was created by the impact of a giant meteorite; the second, that it was the result of an explosion of superheated steam, caused by volcanic activity far below the surface. If an iron meteorite had created the crater, Gilbert assumed that it would have had to be nearly as big as the crater itself. So what predictions could he test? First, the meteorite should be taking up a lot of space in the hollow of the crater. The volume of the hollow would therefore be less than the volume of the ejected material in the crater rim.

Second, the presence of a large mass of buried iron should affect the behavior of magnets and compass needles. Neither prediction was confirmed. Gilbert concluded that a steam explosion was the only surviving hypothesis, in spite of the fact that no volcanic rocks had ever been found in the area. The meteorites around the crater were simply a coincidence.

Ten years later a very different sort of explorer came along. In 1902 Daniel Moreau Barringer, a successful

mining engineer, heard about the crater. When he learned that small balls of meteoritic iron were randomly mixed with the ejected rocks of the crater rim, Barringer immediately concluded that the crater had resulted from a meteorite impact. If the meteorites had fallen at a different time from the time at which the crater was formed, they would have appeared in separate layers from the ejected rock. Like Gilbert, Barringer assumed that the meteorite which made the crater would have to be extremely large - large enough, in fact, for a major mining bonanza.

Meteor Crater Page 2

Rather than testing his impact hypothesis, Barringer set out to assemble the evidence in support of it. In 1906, and again in 1909, he presented his arguments for the impact origin of the crater to the Academy of Natural Sciences in Philadelphia. The evidence included:

The presence of millions of tons of finely pulverized silica, which could only have been created by enormous pressure.

The large quantities of meteoritic iron, in the form of globular "shale balls", scattered around the rim and surrounding plain.

The random mixture of meteoritic material and ejected rocks.

The fact that the different types of rocks in the rim and on the surrounding plain appeared to have been deposited in the opposite order from their order in the underlying rock beds.

The absence of any naturally occurring volcanic rock in the vicinity of the crater.

In 1908, these conclusions were championed by geologist George P. Merrill. Merrill analyzed a new type of rock discovered by Barringer at the crater, which Barringer called "Variety B". He concluded that it was a type of quartz glass which could only be produced by intense heat, similar to the heat generated by a lightning strike on sand. Merrill also pointed to the undisturbed rock beds below the crater, which proved that the force which created the crater did not come from below.

During the same years, a debate was raging among astronomers about the origin of the craters on the moon. As with the Barringer crater, most astronomers initially assumed that those craters were volcanic. Gilbert himself, ironically, was one of the first to argue for an

impact origin, in a paper published in 1893. In 1909, a German geologist advanced the same theory, based in part on the evidence presented by Barringer for the Arizona crater. One objection to the idea of an impact origin for the lunar craters was the fact that all lunar craters are round. Astronomers assumed that most meteorites would have struck the moon at oblique angles, producing elongated craters. Barringer, however, had experimented by firing rifle bullets into rocks and mud, and had discovered that a projectile arriving at an oblique angle would nevertheless make a round hole. In 1923, Barringer's 12-year-old son Richard published an article in Popular Astronomy, using his father's rifle experiments to argue for the impact

Meteor Crater Page 3

Known impact craters of North America. Barringer Meteor Crater is at arrow.

origin of the lunar craters; Barringer himself repeated the arguments a short time later in the Scientific American. The conclusive arguments in the lunar debate were provided by astronomers such as A. C. Gifford, who demonstrated that the force of an impact at astronomical speeds would result in the explosion of the meteorite. Whatever the original angle of impact, the result would be a circular crater.

Scientists now believe that the crater was created approximately 50,000 years ago. The meteorite which made it was composed almost entirely of nickel-iron, suggesting that it may have originated in the interior of a small planet. It was 150 feet across, weighed roughly 300,000 tons, and was traveling at a speed of 40,000 miles per hour. The force generated by its impact was equal to the explosion of 20 million tons of TNT. In 1946, meteorite collector Harvey H. Nininger analyzed the tiny metallic particles mixed into the soil around the crater, along with the small "bombs" of melted rock within it. He concluded that both types of particles were solidified droplets, which must have condensed from a cloud of rock and metal vaporized by the impact. Here, he believed, was proof that the crater was created by explosion.

Using these methods, meteoriticists have now identified over 150 proven impact sites. Evidence suggests that there have been many thousands of other impacts over the course of the earth's history. Meteorites weighing a quarter of a pound or more hit the earth thousands of times a year. One large enough to form the Barringer crater may arrive as often as once every thousand years.

Meteoroids, Meteors and MeteoritesWhen drifting through space, smaller pieces of space rock are called meteoroids. Most of them are the size of sand or gravel. Eventually, some of these meteoroids cross the path of the Earth. They may enter our atmosphere at a velocity of several miles per second.

Because of their tremendous speed, meteoroids are heated by friction with the air to incandescence, which means they glow red hot or even white hot. They are now called Meteors. The air around the meteor also glows, making it possible to see the meteor from the earth. Most small meteors burn up in the atmosphere, leaving only microscopic fragments to drift down to the earth as dust.

Meteor Crater Page 4

Larger meteors are often able to survive their burning path through our atmosphere, however, and strike the earth. We call these meteorites. Because much of the earth is covered by water, most meteorites are never found. When meteorites manage to fall onto land, it is possible for us to find and study them. This is one way to study our solar system.

Petrified Forest National Park Page 1

Petrified Forest National Park has wonderful examples of historic geology and

preservation of fossils. The park is named for the petrified trees which dot the landscape. Our exploration of this park starts with the deposition of the trees, and

continues with the formation of the silica-rich logs which are preserved for us to study.

Most of the rocks found in the park are part of the Chinle formation (the same

formation we will see a lot of tomorrow). This layer was deposited about 200 million years ago in a warm, moist (tropical) climate. This area was much nearer

to the equator than it is now; plate tectonics have transported this area much farther north since then.

The region was a vast basin with numerous rivers and streams flowing through the

lowland.

A lush landscape with coniferous trees up to nine feet in diameter and towering almost

200 feet into the sky rose above the land. Galleries of trees, ferns, and giant horsetails

grew abundantly along the waterway, providing food and shelter for many insects,

reptiles, amphibians, and other creatures.

Over time, trees fell into the waterways,

knocked down by wind, undercut by water, or killed by insects. Rivers and streams

carried the trees downstream, breaking off branches and roots along the way. Many tree trunks came to rest on the banks

of the rivers while others were buried in the stream channels.1

After the trees were transported downstream and became trapped in shallow waters, fluvial deposits of silt, mud, and volcanic ash from volcanoes to the south

Petrified Forest National Park Page 2

or west buried the logs and cut off the supply of oxygen; decay was thus retarded.

Ground water percolating through the sediments dissolved silica from the volcanic ash. As the silica filtered through the logs, it precipitated from solution as

microscopic quartz crystals in the woody tissues where air, water, and sap were originally present in the living tree. In some logs, cell structure remained intact,

albeit entombed. Where the logs were hollow, woody tissue did not limit crystal growth; large crystals of rose quartz, smoky quartz, amethyst, and other

gemstones or large masses of amorphous (non-crystalline) chalcedony and chert lined the cavity walls. Originally, researchers believed that minerals replaced the

wood fibers. In recent experiments, however, after acid was used to dissolve the minerals, the original woody tissue was visible under a microscope.

As the silica petrified the wood, other elements in the water, such as iron, copper, manganese, and carbon, added tints of red, yellow, orange, brown, blue, green,

purple, and black to the fossilized tissues. In some logs, tunnels and galleries are visible,

the remains of ancient excavations dug by

Triassic insects. The high degree of preservation of the logs and other fossils in

the Chinle Formation is due to favorable conditions, such as warm temperatures, high

moisture, and little or no oxygen, during and after deposition of the sediments.3

Most of the trees decomposed and disappeared, but some of the trees were

petrified, becoming the beautiful fossilized logs we see today. Many of the fossilized logs are from a tree called Araucarioxylon arizonicum. Two

others, Woodworthia arizonica and Schilderia adamanica, occur in small quantities

in the northern part of the park.

At least nine species of fossil trees have been identified from the park; all are now extinct.

Distant volcanoes to the west

spewed tons of ash into the atmosphere, carried by the wind into this

area where it was incorporated into the river sediments. Some logs were buried

by sediment before they could decompose. Ground water dissolved silica from the

volcanic ash and carried it into the logs. This solution formed quartz crystals which

filled hollows, cracks, even the interior of the cells, and sometimes replaced the cell walls.

Petrified Forest National Park Page 3

The resulting fossils show many details of the logs’ original surfaces

and, occasionally, the internal cell structures. Traces of iron and other minerals combined with quartz during the petrification process, created the brilliant rainbow

of colors. Within the larger cracks and hollows the growth of quartz crystals was not limited in size and larger crystals of clear and milky quartz, purple amethyst,

and yellow citrine formed.

This area has endured many changes. As time passed, a thick sequence of younger rock buried the Chinle Formation.1

The Chinle Formation was deposited over 200 million years

ago during the Late Triassic Period. The colorful badland hills, flat-topped mesas, and sculptured buttes of the Painted Desert

are primarily made up of the Chinle Formation, mainly fluvial

(river related) deposits. Within Petrified Forest National Park, the Chinle Formation is further divided to include the Blue Mesa

Member, the Sonsela Member, the Petrified Forest Member, and the Owl Rock Member.2

Over millions of years, the region was uplifted as part of

the massive Colorado Plateau. Wind and water eroded the land, removing the younger layers of rock and exposing parts of the

Chinle Formation. Now fossilized logs that were once embedded in the Chinle Formation lie strewn across the clay hills and

are exposed in cliff faces. You might notice that most of the logs are broken into segments.

People did not cut the logs. Because the sections are still in

order, we know that the logs fractured after they were buried and the petrification process was complete. Composed of quartz, petrified logs are

hard and brittle, breaking easily when subjected to stress. Softer sedimentary

layers surround the hard logs. As the sedimentary layers shifted

and settled, stress on the rigid logs caused fractures. Some

researchers believe that such stress may have been produced by

earthquakes or the gradual uplifting of the Colorado Plateau.1

Erosion continues today. Rain

and wind wear away the land, uncovering additional logs, while freezing and thawing break down the logs exposed on the surface. With the infinite patience of

time, the layers of sediment will continue to erode, exposing more pages of this ancient history book.

Petrified Forest National Park Page 4

Sources

1. https://www.nationalparkstraveler.org/parks/petrified-forest-national-park/geology-petrified-

forest-national-park.

2. https://www.nps.gov/pefo/learn/nature/geologicformations.htm

3. Arizona Geology, Spring 1989

Dino Tracks at Tuba City - Dilophosaurus Page 1

THE DISCOVERY OF DILOPHOSAURUS The following is an interview given by the discoverer of Dilophosaurus, Sam Welles (courtesy Cal Berkeley Web Site)

In the summer of 1942 Dr. Camp and I were on a joint expedition into the Navajo country. He was working in the Permian beds of Monument Valley and I in Moenkopi beds near Cameron.

AT THE END OF SUMMER after finding a lot of material in both of these lower formations, Dr. Camp had to return to Berkeley, and he asked me to look up the report of a skeleton found in the Kayenta Formation, which might possibly be dinosaurian.

I TRIED TO FIND THIS and failed, and went to see Richard Curry, who was then the owner of the trading post at the foot of the Tuba City grave. He got hold of

Jesse Williams, a Navajo who had discovered these bones in 1940, and they both took me out to this site, and with Bill Rush and Ed Kott, we set up camp and decided to go ahead and excavate.

THERE WERE THREE DINOSAURS in a triangle about twenty feet apart and one was almost worthless having been completely eroded. The second was a good skeleton showing everything except the front part of the skull.

THE THIRD GAVE US THE FRONT PART OF THE SKULL and much of the front part of the skeleton. These we collected in a ten day rush job, loaded them into the car, and brought them back to Berkeley.

THE SPECIMEN WAS BROUGHT TO BERKELEY and cleaned up by a WPA project under Dr. Ron Langston. It took three men two years to clean and prepare the skeleton and then make a wall mount of the animal. We knew it was new, and in 1954 I published a preliminary description naming it Megalosaurus. We didn't know how new it was.

IN 1964 I BECAME CONCERNED OVER THE AGE OF THE ANIMAL. It was based on differences of opinion as to whether the rock were of Triassic or Jurassic age (as I had said).

SO I RETURNED and yes, the rocks were of Kayenta formation. About a quarter mile south of the original find I found a fourth skeleton which turned out to be a very fine skeleton of an adult animal.

IT WAS THIS SKELETON, that on preparation in our laboratory showed very clearly that the animal had a double crest and that the name should be changed from Megalosaurus. We proposed the new name of Dilophosaurus, based on the double crest on top of the head. The original skull also shows the crest, but we had not recognized it. The two crests had been crushed together, and we had assumed they were part of a cheek bone that had been pushed out of place.

The skull of Dilophosaurus tells us the most about the animal's relationship to other ceratosaurian theropods. It is pictured at right -- the front of the snout is to your right; the top of the skull is at the top of the picture. You are

Dino Tracks at Tuba City - Dilophosaurus Page 2

looking at the right side of the best-preserved skull of Dilophosaurus ; as Sam Welles will tell you, the holotype specimen did not have a complete skull, while a later find had this beautifully preserved skull that revealed to Sam that this was a new type of dinosaur. The dentary (lower jaw) is not present in the image above. Now look closely at the skull . The premaxilla (at the tip of the snout) is loosely attached to the maxilla (to the left of the premaxilla; it is the primary tooth-bearing bone of the upper jaw). This is a diagnostic characteristic of most ceratosaurs. Sam

will tell you more about the way it might have worked in the living animal. Also note the thin crest on the top of the skull; this immediately showed Sam Welles that he had discovered a previously unknown theropod dinosaur. Dilophosaurus wetherilli was a fairly large ceratosaur; about 6 meters (20 feet) long, and quite slender. It is not the largest or most well-studied ceratosaur, but it is represented by some of the most complete specimens of any known ceratosaur, with good preservation --considering their 150-odd million years of age. UCMP is very proud of its wonderful and unique specimens of Dilophosaurus; we possess the only 3 known remains of this interesting dinosaur

HE WAS A VERY POWERFUL ANIMAL. He probably stood about eight feet high -- body about the weight of a small horse with long, strong hind legs; forelimbs with hand that were flexible, with an opposable thumb... much like we have, so he can grasp a prey.

HIS HIND LEGS, HIS FEET, WERE ARMED WITH VERY POWERFUL CLAWS and were probably used as weapons as well as for locomotion. He was bipedal of course, and probably a very rapid runner.

I DONT KNOW THE SIGNIFICANCE OF THE CRESTS, probably ornamental. The strange thing about the

animal is the attachment of the premax (at the tip of the upper jaw) to the maxillary (main upper jaw) bones... a very weak attachment such that the very sharp teeth could not have been used very much for stabbing. They could have been used for plucking.

HE WOULD HAVE HAD TO KILL, IF HE KILLED, with his hands and feet, and then pluck the meat from the carcass. He was probably a group animal, in that we found three together. They probably moved around in small herds of family groups, covering a lot of territory because of the ability to travel and to move rapidly.

Dino Tracks at Tuba City - Dilophosaurus Page 3

On Dilophosaurus, the actor...(based on the appearance of the dilophosaurus in Jurassic Park, specifically when Dennis Nedry [the weight-challenged computer programmer] was attacked by the venom-spitting dino).

IT WAS QUITE A THRILL TO SEE DILOPHOSAURUS AS AN ACTOR IN JURASSIC PARK. He came on strong. The only two things I would question were his ability to spit poison forward. We have no evidence of there being poison. . . ...AND THE OTHER THING IS THE ERECTION OF THE NECK FRILL. The cervical vertebrae on Dilophosaurus are very long, and they are one under the other, making a very strong support down the side of the neck.

AND THERE IS ALSO A SHORT ANTERIOR PROJECTION of these vertebrae (or ribs) which would make it impossible for the animal to erect a crest.

THESE ARE MINOR POINTS and these are good showmanship. I enjoyed the movie thoroughly and was very happy to find Dilophosaurus an internationally known

actor.

Tuba City Dino TracksTraces of this dinosaur have only been found in Arizona. The tracks tell us a great deal about Dilophosaurus;

how it moved, how big and how fast it was, and whether it traveled in groups or in solitary.The tracks are found in sandstone. This sandstone was wet and muddy at one time, and dinosaurs (and other

creatures) left their prints as they walked or ran across the muddy ground. Later, this ground was buried by many other sediments and turned into rock. The rock was then lifted, eroding the rock layers above it to expose the fossilized tracks.

There are several Jurassic-age track sites west of Tuba City, AZ on Navaho Tribal Lands. They are relatively easily accessible from the roadand recommended by National Park personal if you are looking for dinosaur tracks to view. Three different ichnogenera can be seen in this area: Dilophosauripus williamsi, Kayentapus hopii, and Hopiiichnus shingii. All are probably tracks of theropod dinosaurs. Dilophosauripus and Kayentapus are

similar in size 27-34 cm in length, while Hopiichnus is approximately 10 cm in length. They occur in the Jurassic age Kayenta formation.

Close-up view of fossilized bones of the therapod, dilophosaurus, which make the tracks shown at right.

Wupatki Atmospheric Blowhole Page 1

The Flagstaff area has a number of holes in the ground from which air from underground chambers blows at speeds approaching 30 mph. Depending on atmospheric conditions, air can also be sucked into the ground at the same speed. There are five known blowholes in the region, of which three are located in Wupatki National Monument.

Wupatki is famous for its fairly well preserved Indian ruins, but the geology claim-to-fame is from the blowholes here. From 800 A.D. to about 1000 A.D. the Sinagua Indians colonized the area around these blowholes; they considered these blow holes sacred. The temperature of the air that is blown out of the blowholes is consistent throughout the year. In the summer heat, these blow holes would blow 50 degree air. They discovered natural air conditioning. In the winter, when temperatures were below freezing, the 50 degree air was like a natural heater.

Blowholes such as this are fairly rare. It requires a large underground cave system with very limited access in order to form a blowhole. Geologists have estimated that the size of the underground cavern system has a minimum volume of 8 million cubic feet. This is the same volume as a building that covered a 100 yard football field that was 42 miles high.

Exploration of the cave system is not possible at the present time. The only access to the cave system is via the blowholes, which are too narrow for exploration.

The caverns are formed in limestone when groundwater dissolves the calcium carbonate forming voids in the rock. If the area is lifted above the water table (or if the water table drops), the voids become air chambers (or caves). In order for blowholes to exist, small cracks must exist that extend from the underground caves to the surface.

The blowholes blow air out or suck in air depending on the atmospheric pressure at the surface. Air pressure naturally cycles throughout the day. Generally speaking, surface air pressure is lower during the day and higher at night. Since air travels from high pressure to low pressure, the blowholes generally blow air out during the day and early evening, and suck air in during the

Side view of the area’s geologic structure. Cavern structure is not known at this time, but the volume of the caverns has been estimated at a minimum of 8 billion cubic feet.

Wupatki Atmospheric Blowhole Page 2night and early morning. The graph below shows the correlation between surface air pressure and the speed and direction of the wind exiting or entering the blow hole.

The graph on the left shows a definite correlation between air pressure and wind speed and direction.

There are usually two periods during the day when the surface pressure is equal to the pressure inside the underground cavern. When this occurs, no air leaves or enters the blowhole. Local weather conditions can also have an effect; thunderstorms in the vicinity can lower surface air pressure significantly and cause high speed winds to exit the blowhole.

Eventually, erosion of the Kaibab Limestone and Moenkopi Sandstone will create a surface opening of the caverns, and opening up one of the largest cavern systems in North America. This may take many thousands of years to occur however.

Text and Diagrams from a Rand Corporation Memorandum RM-3139-RC, June 1962; Meteorological-Geological Investigations of the Wupatki Blowhole System; J.D. Sartor and D.L. Lamar

Sunset Crater Page 1The most recent eruption in the San Francisco

Volcanic Field began about 930 years ago and produced a cinder cone known as Sunset Crater, about 15 miles northeast of Flagstaff. It is just one of more than 600 cinder cones around Flagstaff.

When the Sunset Crater eruption began, the surrounding area was inhabited entirely by Native Americans. These people did not have our scientific instruments to record the earthquakes that are always precursory to volcanic eruptions. Still, the fact that no human bodies buried by Sunset Crater

cinders have been discovered suggests enough understanding of what was happening to get out of harm's way. Immobile objects, however, like pit houses, were buried by cinders that blanketed the area around the new volcano. Life near Sunset Crater must have been desirable, though, because pit houses built on top of the cinder blanket indicate the area was reinhabited not long after eruption ceased.

There is no human-recorded account of the eruption story, but the annual growth rings of ponderosa pines that grew near the site where the volcano formed record the timing of the eruption about as clearly as any historian might have from first-hand observations.

Beams of ponderosa pine were used in construction of the pit houses. Careful examination of growth rings still evident in these prehistoric beams allow scientists to precisely determine the year the tree was cut. Experts in dendrochronology (the study of annual growth rings of trees) tell us that the youngest ring found in beams of buried houses records the growing season of A.D. 1046. On the other hand, the oldest growth ring in beams of post-eruption houses records A.D. 1071. Thus, the eruption must have occurred after A.D. 1046 but before A.D. 1071.

Growth rings are also sensitive indicators of growing conditions. When dendrochronologists studied several trees damaged (but not killed) by the eruption, they found the rings up to and including 1064 to be normal, whereas rings for 1065 were much thinner than in preceding years. Thus, they concluded that eruption began after the 1064 growing season but before the 1065 season. A subsequent several-year period of rebound to a normal annual tree-ring pattern indicated gradual recovery from the initial eruption trauma.

A popular misconception is that the entire eruption occurred at Sunset Crater, but the story is more complex. Geologists who have carefully studied the area conclude that the eruption began with lava fountaining from a 6 to 9 mile-long, northwest-trending fissure. This style of eruption is known as a curtain of fire (right). After the initial fissure phase, the eruption concentrated at the northwest end of the fissure, where the Sunset Crater cinder cone grew. Such an evolution, from fissure to central focus, is quite common for basaltic eruptions, and typical of the kind of magma that forms cinder cones.

Sunset Crater Page 2Experts disagree on the duration of eruption, but available evidence suggests that phases

after the initial outburst occurred intermittently for about 150 years. This evidence comes from the fact that all volcanic rocks contain small grains of magnetic minerals that are pulled into alignment with the Earth's magnetic field, just as the needle on a compass is pulled to point toward magnetic north, as magma solidifies to rock and cools. In addition, the position of the Earth's magnetic pole is known to move continuously at a rate that leaves a decipherable record of this movement in volcanic rocks if the rocks span at least 100 years. Rocks that span the entire period of the Sunset Crater eruption suggest a change in magnetic field direction, but change so near the limit of the measurement technique that skeptics can reasonably argue a contrary position.

Whatever the exact eruption duration, while inhabitants of England were fleeing attacks by William the Conqueror from Normandy in 1066, the residents of northern Arizona probably were fleeing a downpour of volcanic cinders from Sunset Crater. Local inhabitants almost certainly watched many fiery eruptions between about 1064 and 1200. Given innate human curiosity about the unusual, these shows may have been a drawing card for audiences from a broad region of the southwest.

Sunset Crater was saved from destruction in the 1920’s when H.S. Colton, founder of the Museum of Northern Arizona and a prominent Flagstaff resident, thwarted the attempt of a Hollywood movie company to simulate an eruption by placing large charges of explosives in the cinder cone. Such protection is now provided by the site's national monument status. Visitors today are no longer allowed to climb Sunset Crater.

One of the questions inevitably asked of geologists during interviews is whether or not there will be another eruption in northern Arizona. The answer from a geologic perspective: almost certainly.

It is presumptuous for humans, whose tenure on Earth is so short, to assume that the process that produced several hundreds of eruptions spread over the past 6 million years, including one that began just 930 years ago, is now inactive. An accurate forecast of when and where the next eruption will occur is impossible. But nature has already provided enough clues for one to make an educated guess about where. And precursory earthquakes, early warnings to all volcanic eruptions, will provide a more accurate call on the where and will essentially define when.

The concepts of momentum and inertia provide help in understanding the geologic perspective on volcanism in northern Arizona. Simply restated, these basic concepts of physics say that a massive body tends to stay in a given state of motion, be it at rest or moving. Thus, it is unlikely that 6 million years of producing hundreds of eruptions within a fairly restricted part of northern Arizona has run its course with the formation of Sunset Crater.

To properly appreciate the geologic perspective, one must think in terms of geologic time. The Earth is about 4.6 billion years old, an age that most people (understandably) find difficult

Sunset Crater Page 3to relate to human events. Even 930 years, the period since the beginning of the most recent eruption near Flagstaff, is an eternity compared to the typical human life span. So, it is not surprising that most people think of the volcanic area around Flagstaff as extinct, or at least in deep dormancy. Precisely because of the vast difference in scale between geologic time and human-life time, geologists have pondered for generations over whether to classify Sunset Crater and similar volcanoes as extinct, dormant, or active.

The bottom line: Sunset Crater can be classified as either dormant or active, but however one chooses to think of it, future eruptions in the vicinity are expected sometime in the near future geologically speaking.

Whether or not you believe that another volcano will erupt near Flagstaff, it's worth knowing something about how magma announces its pending arrival and eruption. The well-documented eastward migration of active volcanism during the past 6 million years from near Williams to Sunset Crater suggests that the next eruption will be in the vicinity, or to the east, of Sunset Crater. A precise location for the next eruption is impossible to define until magma rising toward the Earth's surface triggers

precursory earthquakes, as crustal rocks are cracked and shouldered aside to make room for magma to rise. Earthquakes of this sort are generally too weak to be felt, unless one happens to be directly over the source of shaking. However, the upward path of magma intrusion can be charted with seismometers, sensitive electronic recording instruments. Enough seismometers are now in place across northern Arizona to provide an early warning of rising magma. One such instrument is on display at the Visitor Center at Sunset Crater Volcano National Monument.

If many earthquakes originate at successively shallower depths beneath a small geographic area, this suggests the ascent of magma beneath that area. In addition to many discrete small earthquakes, magma pulsing upward through the Earth's crust commonly causes steady earth shaking, called volcanic or harmonic tremor, which can last minutes to hours. When they occur together, upward-migrating earthquakes and harmonic tremor are strong evidence that magma is on the rise.

Based on studies of volcanic areas around the world, the time between onset of such earthquakes and eruption is likely to be on the order of days, weeks or even months. Lest this seem like frighteningly little advance warning for us to adequately react to the threat of a volcanic eruption, remember that the possibility of any eruption near Flagstaff during our lifetime is too small to lose sleep over. Meanwhile, infrequent and isolated earthquakes in northern Arizona record not magma movement but normal restlessness of the Earth's crust.

Duffield, Wendall A.; Volcanoes of Northern Arizona; pages 31-37. Grand Canyon Association1997, Grand Canyon, Arizona