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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