Physical Geography: Landforms of California

Overview

• Geologic Time

• Movements of the Continents

• Earth Materials

• Tectonic Forces

• Weathering and Erosion Processes

• Erosional Agents and Deposition

Geologic TimePretend the age of the earth (4.6+ billion years) is

compressed into one calendar year.

January 1 - Earth and planets formed

Early March - liquid water stands in pools.

Late March - earliest life

July - oxygen is important part of atmosphere

October 25 - multicellular organisms

Late November - plants and animals abundant

December 15 to 25 - dinosaurs arise and disappear

11:20 pm, December 31 - Humans appear

One second before midnight - Automobile invented

• General trends: temperature, density • Horizon composition, behavior

The Earth’s Interior

Distance: 6730 km (3963 miles)

Earth Materials

• Three major rock types– Igneous– Sedimentary– Metamorphic

Igneous Rocks

• Igneous (ignus = fire)

• Formed from the cooling of molten rock (magma/lava), a process called crystallization.– Slow cooling larger crystals > dense rock– Rapid cooling small crystals > lighter rock

• Two classes of igneous rocks– intrusive: formed inside the Earth– extrusive: formed at Earth’s surface

Igneous Intrusive Rocks• Cools slowly (thousands of years)

• Visible crystals

• Examples

- granite - diorite - gabbro

Igneous Extrusive Rocks• Cools rapidly - exposed to surface

• No visible crystals

• Examples

- rhyolite - andesite -basalt

Typical Igneous Intrusions

Know: Batholith and Dike

Exposed Batholiths

Sierra Nevada, CA

Sedimentary Rocks

Compaction Cementing

Sedimentary Rocks

Formation

Relative Abundance by Type

Sandstone (larger grains)

Shale (fine grains)

Limestone (CaCO3)

Where do Sedimentary Rocks Form?

Terrestrial environments (non-marine) Rivers and floodplains

(fluvial environment)

Lakes

Deserts (aeolian environment)

Marine environments Continental shelf

Continental slope and rise (deep sea fans)

Abyssal plain

Beach and barrier islands

Metamorphic

Gneiss (broad foliation)

Schist (narrow foliation)

The Unstable Landscape: California Plate Tectonics

• Crustal Processes– Destruction (subduction)– Creation (volcanism )– Alteration / deformation (folding and faulting)

Introduction

• Plate boundaries: main location for Earth’s volcanic and earthquake activity.

• Type of plate boundary determines activity.

• 3 types– diverging (spreading)– converging (colliding)– transform (sliding past each other)

Convergent Plate Boundaries• Action:

– collision; destructional or constructional

• Activity: – depends on type of convergence– 3 types: ocean-continent, ocean-ocean, cont.-cont.

Convergent: Ocean-continent• Action:

– collision; destructional (subduction of ocean plate)

• Activity: – shallow to deep earthquakes; volcanism (continental)

• Features: – ocean trench; volcanic mtns on continental margin

Volcanoes: Explosive• Composite cones (stratovolcano)

– pointed, steep-sided, tall volcanoes

– “Composite”: layers of pyroclastics and lava (mostly felsic)

– Explosive and dangerous; found near subduction zones

Volcanoes: Explosive

Arenal, Costa Rica

Mt. Shasta, California Mt. Lassen, California

Crustal Deformation:Folding, Faulting, and Earthquakes

Introduction

• Crustal Processes– Destruction (subduction)– Creation (volcanism - convergent/divergent)– Alteration / deformation (folding and faulting)

Crustal Deformation

• Outcome / result of “battle”: Stress v. strain (force v. resistance)– Stress: force imposed on the rock

(tension, compression and shear)– Strain: how the rock responds to the stress

(folding / bending or faulting / breaking) Is the rock brittle or ductile?

Figure 12-7

Faulting• Definition: fractures where some type of

displacement (movement) has occurred along a break in rock.

• Three types– normal

– reverse/thrust

– transform (strike-slip)

Carmel Valley Fault, CA

Normal Faults

• Tensional stress• Earthquake and displacement along fault plane fault scarp

Landforms - Normal Faulting

Owens Valley, CA

Sierra Nevada, CA

Grand Tetons, WY

Basin and Range

• Horst and graben (“hill” and “grave”)

Death Valley/ Panamint Ranges

Why saline?

Landforms: Normal Faulting

• Grabens (“Graves”)

Bas

in a

nd R

ange

Transform Plate Boundary

• Action: – shear (lateral motion)

– no loss/gain of plate material

San Andreas fault system – How long is it? About 1000 km – Relative motion of the Pacific

Plate? @ 2 inches (5 cm) northwest per year. In 10 million years Los Angeles will be off of San Francisco .

San Andreas Fault System - Southern California

Transform Plate Boundary• Activity:

– shallow to moderate earthquakes – little to no volcanism

http://quake.usgs.gov/recenteqs/

Tremblor Range

Dragon’s Back

Carrizo Plain, CA (view to the east)

Transform Plate Boundary

• Features:– shallow, linear

rift valleys– sag ponds

San Andreas Lake (Crystal Springs Reservoir) - looking south along fault

- San Francisco water supply - geology vegetation

Carrizo Plain, central CA

Transform Plate Boundary

• Features:– offset streams, objects

Stream channel offset, Carrizo Plain,

central CA1906 earthquake offset, Point Reyes, CA

The Geography of Earthquakes

• USA: 1977-1997 earthquake events

• USA: every state except ND, FL

The Geography of Earthquakes

• Globally: primarily at plate boundaries

• Intraplate earthquakes do occur!

Mag 6.5

Earthquakes• Earthquakes are the shaking or vibration of

the ground as a result of rocks suddenly breaking along a fault.

• Focus (hypocenter) = rupture point

• Epicenter = point on surface above focus

• Foreshocks

• Aftershocks

Process: the earthquake cycle (elastic rebound theory)

• Earthquakes are a ‘release of energy’ in the form of a seismic wave (vibrates the crust).

• Plate movement strain builds rocks “locked together” (frictional bond)

• Rocks bend hit limit --> rupture/break

• Cycle repeats ”start-stop” motion along fault

Seismic waves• Some of the waves that are generated by an

earthquake travel within the earth and other travel along the surface, creating surface waves.

• Waves traveling within the earth are known as body waves.

Surface Waves

• Surface waves cause the most damage to buildings during an earthquake.

• Surface waves can set up liquefaction in wet alluvium. This is where the most extensive damage to buildings occurs.– Liquefaction: wavelike, almost liquid, rolling of

surface– Alluvium: fine material deposited by water

over many years.

Measuring Earthquakes• seismograph: records the vibrations

of the crust

• Richter Scale measuresvibration, not damage.

• seismogram: tracing record

Major California Earthquakes

• Fort Tejon, 1857 - 8.0 magnitude

• San Francisco, 1906 - 7.9 magnitude

• 1933 Long Beach - 6.3 magnitudeDestroyed Glendale College Buildings!

• San Fernando, 1971 - 6.6

• Northridge, 1994 - 6.7

• Hector Mine, 1999 - 7.1

Fort Tejon, 1857

• TIME: January 9, 1857

• LOCATION: 35° 43' N, 120° 19' W• about 72 km (45 miles) northeast of San Luis Obispo

about 120 km (75 miles) northwest of Bakersfield,as shown on the map (epicenter location uncertain).

• MAGNITUDE: Mw 8.3 (approx.)

• TYPE OF FAULTING: right-lateral strike-slip

• FAULT RUPTURED: San Andreas fault

• LENGTH OF SURFACE RUPTURE: about 360 km (225 miles)

• MAXIMUM SURFACE OFFSET: about 9 meters (30 feet)

San Francisco Aftermath, 1906

Magnitude: 7.9

San Francisco, 1906 Magnitude: 7.9