Physical Geography Chapter 13: Introduction to Landform Study Outline
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Transcript of Physical Geography Chapter 13: Introduction to Landform Study Outline
Chapter 13: Introduction to Landform Study
The Structure of Earth
The deepest existing mine shaft goes down 2.4 miles
Deepest drills for samples goes down 8 miles
Earth’s 4 Interior shells/regions:o The Crust-
Broad mixture of rock types Beneath oceans the crust is 4 miles (average) Beneath the continents the crust is 40 miles (average) Makes up less than 1% of Earth’s volume and 0.4% of Earth’s mass Has change in mineral composition at base [called Mohorovičić Discontinuity
(Moho)]o The Mantle-
Extends downward to approximately 1800 miles The largest of the 4 shells Makes up 84% of total volume and 2/3 of Earth’s total mass Three sub layers-
Lithosphere -o Thin yet hard and rigido 40-60 miles deepo Temperature believed to reach 1,832°F
Asthenosphere -o Rocks are hot and loose much of their strength and become
plastic (easily deformed, like tar) Centrosphere (lower mantle) -
o Rocks are believed to be largely rigid/firm againo Plays a major role in controlling the thermal evolution of the
planet
o The Outer Core- Molten Liquid Extend to depth of 3100 miles Thought to be made of iron/nickel or iron/silicate
o The Inner Core- Thought to be made of iron/nickel or iron/silicate Solid and very dense mass Radius of 900 miles
Earth’s Magnetic Field-o Primarily in the outer coreo Changes over timeo The location of the North Magnetic Pole does NOT match the geographic location of the
North Pole Slowly shifts several tens of kilometers each year
o Every couple of thousands of years, the polarity of the Earth’s magnetic field reverses (North becoming South)
Plate Tectonics and the Structure of Earth-o Earth’s Plates are slowly moving over the warm, soft asthenosphere below.o The plates are literally pulling apart, colliding, and sliding past each othero Volcanic Activity, Faulting, and Folding are linked to the plate action
The Composition of Earth
100 natural chemical elements are found in Earth’s crust, mantle, and core
Minerals - Naturally formed compounds and elements of Earth
Minerals Must Be-o A solido Naturally found in natureo Inorganico Have a specific chemical composition wherever found that varies only within certain
limitso Contain atoms arranged in a regular pattern to form solid crystals
The majority of known minerals are found only in the crust
The Families of Rock-Forming Minerals-o Silicates-
The largest and most important mineral family Combine Oxygen (O) and Silicon (Si) Hard and durable Major subcategories-
Ferromagnesian Silicateso Olivine
Nonferromagnesian Silicateso Quartz
They are distinguished by the presences or absence of iron and magnesium in their composition
Feldspar and quartz are the most abundant of the silicate minerals Quarts is composed of pure silica (SiO2)
o Oxides- An element combined with oxygen Megnetite
o Sulfides- Composed of sulfur in some combination with one or more other elements
Galenao Sulfates-
Contain sulfur and oxygen with some other element Gypsum
Calcium is the principle combining element Usually light-colored Mostly found in sedimentary rocks
o Carbonates- Light colored or colorless Composed of one or more elements in combination with carbon and oxygen Calcite
o Halides- Notably salty Flourite
o Native Elements- Discrete Elements - Not combined chemically with another element
Gold/Silver
Rocks
Rock - Solid material composed or aggregated mineral material
Outcrop - Solid rock found right at the surface
Rocks-o Solid rock exist as a buried layer of bedrock and covered by a layer of broken rock
(regolith) Soli comprises the upper portion of regolith
Three Major Rock Classes-o Igneous-
Formed by the cooling and solidification of molten rock Magma - Molten rock beneath the surface
The amount of silica present is an important variable to magma composition
Magmas with large amounts of silica cool to form felsic igneous rockso Contain large portions of light-colored silicate minerals
(quartz/feldspar)o Have lower melting temperatures than mafic minerals
Magmas with low amounts of silica cool to form mafic igneous rockso Contain large portions of dark-colored, magnesium- and iron-
rich silicate minerals (olivine/pyroxene) Lava - Molten rock when it flows out on, or is squeezed up onto, the surface Form directly from the cooling of magma or lava
Although some develop from the welding of tiny pieces of solid volcanic rock, called pyroclastics
Texture of igneous rock is determined by where/how the molten material cools The slow cooling beneath the surface leads to a coarse-grained texture The rapid cooling of lava on the surface leads to a fine-grained texture
Two Main Igneous Rocks Categories- Volcanic/Extrusive Igneous Rocks-
o Form from the cooling of lava or the bonding of pyroclastic materials on the surface
o Form on surface of Eartho Complete within hourso Mineral crystals in volcanic rocks as small (almost invisible)o Volcanic rocks that form from the accumulation of pyroclastics
may clearly show tiny fragments of shattered rock (from explosive volcano)
o Basalt - Black/dark gray Forms from cooling of lava Fine-grained rock Comprised of only dark minerals (plagioclase feldspar…) Makes up the bulk of the ocean floor crust
o Obsidian - Type of volcanic glass (no organized crystal material) Black in color Forms from extremely rapid cooling of lava
o Pumice - Forms from the rapid cooling of frothy, gas-rich, molten
material Light enough to float on water
o Tuff - Volcanic rock Consists of welded pyroclastic fragments
Plutonic/Intrusive Igneous Rocks-o Form from the cooling of magma below the surfaceo Cool and solidify beneath the Earth’s surfaceo Surrounding rocks serve as insulation around the intrusion on
magma that greatly slows the rate of coolingo Thousands of years to complete coolingo Individual crystals in plutonic rocks can grow to a large sizeo Granite -
Light colored Coarse-grained igneous rock Made of a combination of light & dark colored minerals
(quartz, plagioclase feldspar, potassium feldspar, …) Make up the core of many mountain ranges
o Sedimentary- The disintegration of rocks produces fragmented mineral material (Figure 1)
Removed by water/wind/ice/gravity/etc… much of the material is transported by water moving as sediment
Sediment is eventually deposited in a quiet body of water (floor of the ocean)
Over a long period of time sedimentary deposits build in thickness It exerts enormous pressure Causes individual particles in the sediment to adhere to each other and
to interlock Chemical cementing takes place
o Silica, calcium, carbonate, and iron oxide precipitate from the water into the pore spaces in the sediment
This transforms the sediments to sedimentary rock Most sedimentary deposits are built up in more or less distinct horizontal layers
(strata) Vary in thickness and composition Parallel structure
The strata may later be uplifted, tilted, and deformed by pressures from within the Earth
Two subcategories of sedimentary rocks- Clastic/Detrial Sedimentary Rocks -
o Sedimentary rocks composed of fragments of preexisting rocks in the form of cobbles, gravel, sand, silt, or clay
o Shale/Mudstones- Composed of very fine silt and clay particles
o Sandstones- Made up of compacted, sand-size grainse
o When the rock is composed of rounded, pebble-size fragments it’s called conglomerate (Figure 2)
Chemical & Organic Sedimentary Rocks -o Formed by the precipitation of soluble materials or more
complicated chemical reactiono Limestone is the most widespread result
Can be formed from the accumulated skeletal remains of coral and other lime-secreting sea animals
o Organically accumulates sedimentary rocks (like coal) are formed from the compacted remains of dead plant material
o Metamorphic- Igneous or sedimentary rocks that have been drastically changes by heat and/or
pressure
Figure 2
Figure 1
The effects of heat and pressure on rocks are strongly influences by such things as the presence or absence of fluids in the rocks and the length of time the rocks are heated and/or subjected to high pressure
Metamorphism can cause its mineral components to be recrystallized and rearranged
As a result the rocks are changes in structure, texture, composition, and appearance
Metamorphism can occur beneath the surface of the Earth where magma comes in contact with surrounding rocks (altering the surrounding rocks through heat and pressure)
Regional Metamorphism takes place where large volumes of rock deep within the crust are subjected to heat and/or pressure over long periods of time
Foliated - If the minerals in a metamorphic rock show a prominent alignment or orientation
May have platy, wavy, or banded texture Some rock change in predictable fashion when metamorphosed
Sandstone → Quartzite Shale → Slate
Metamorphic rocks are identified according to their physical characteristics and appearance
The Rock Cycle
The Study of Landforms Landform - An individual topographic feature of any size (cliff –mountain range)
Geomorphology - The study of the characteristics, origin, and development of landformers
70% of our Earth is covered with oceanic waters
58 million square miles of land are scattered over the continents and innumerable islands
Basic Elements for an analytical approach:o Structure-
The nature, arrangement, and orientation of the materials making up the landform being studied
o Process- Considers the actions that have combined to produce the landform
o Slope- The Fundamental aspect of shape for any landform
o Drainage- The movement of water either over Earth’s surface or down into the soil and
bedrock
Some Critical Concepts
Relief - The difference in elevation between the highest and lowest points in an area
Internal Processes-o Originate from within eartho Energized by internal heat that generates forces that apparently operate outside of
any surface or atmospheric influenceso Resulting in crustal movements (folding, faulting, and volcanic activity)o Increase the relief of the land surface
External Processes-o Draw their energy mostly from sources above the lithosphere (in the atmosphere or in
the oceans)o Behavior often predictableo Behavior influenced by the existing topographyo Thought of as wearing-down or destructive processes (called denudation)
Uniformitarianism-o Put forth by James Hutton in 1795o Means that the processes that are shaping the contemporary landscape are the same
processes that formed the topography of the past
Geologic Time-o Refers to the vast periods of time over which geologic processes operate
Scale and Pattern
A prime goal of any geographic study is to detect patterns in the areal distribution of phenomena