Geography 417
California for Educators

Lesson One

California’s Landforms

Landforms

• In order to understand much about California, it is important to understand some of the basic processes related to the construction of California’s topography.

• Landforms directly affect climate and precipitation, agriculture, mining, industry.

• Indirectly affect culture, religion, economy and a host of other items.

Mountains

• Of what are the mountains made?

• What various processes contributed to the formation of California’s mountains?

Geologic Time

Pretend 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

Geologic Time (fig)

Mesozoic California (figure)

Dinosaurs

• Why don’t you find many dinosaur fossils from the Mesozoic period in California?

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 Þ larger crystals > dense rock

– Rapid cooling Þ 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

Exposed Batholiths (figure)

Sills and Dikes (figure)

Sedimentary Rocks

• Rocks that have formed from sediments (dirts) that have been compacted and cemented to form rock.

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

Sedimentary Rocks (figure)

Sedimentary Rocks

• Relative Abundance by Type

Sedimentary Rocks (figures)

Metamorphic Rocks

• Metamorphic rocks are rocks formed from either sedimentary rock or igneous rock, but have over time and under enormous heat and pressure metamorphosed into a structurally and chemically new rock type.

Metamorphic Rocks

Metamorphic Rocks
or That’s very Gneiss, but I don’t give a Schist!

Rock Cycle (fig.)

Plate Tectonics

• Plate tectonics is the process by which mountains in California and elsewhere are formed.

• The movement of plates are also responsible for California’s earthquakes.

Plate Tectonics

• 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)

fig

Crustal Processes

• Destruction (subduction)

• Creation (volcanism )

• Alteration / deformation (folding and faulting)

Convergent Plate Boundaries

• Action:

– collision; destructional or constructional

• Activity:

– depends on type of convergence

– 3 types:

• ocean-continent

• ocean-ocean

• cont.-cont.

Convergent Plate Boundaries (figure)

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

Convergent: Ocean-continent

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-different than shield volcanoes (Hawaii)

Cascade Volcanoes (figures)

Shasta (figures)

Lassen (figures)

Crustal Deformation:
Folding, Faulting, and Earthquakes

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?

Faulting

• Definition: fractures where some type of displacement (movement) has occurred along a break in rock.

Three types

– normal

– reverse/thrust

– transform (strike-slip)

Normal Faults

• Tensional stress

• Earthquake and displacement along fault plane creates fault scarps

Landforms - Normal Faulting (figures)

Basin and Range

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

• Death Valley/ Panamint Ranges

– Why saline?

Landforms: Normal Faulting

• Grabens (“Graves”)

Transform (strike-slip) faults

Landforms: shallow rift valleys or

long trenches: Salton Trench

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: South

Transform Plate Boundary

• Activity:

– shallow to moderate earthquakes

– little to no volcanism http://quake.usgs.gov/recenteqs/

Transform Plate Boundary

• Features:

– shallow, linear rift valleys

– sag ponds

Transform Plate Boundary

• Features:

– offset streams, objects

San Andreas Fault System - Southern California

Earthquakes: US (figure)

• USA: 1977-1997 earthquake events

• USA: every state except ND, FL

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

Seismic waves

• Some of the waves that are generated by an earthquake travel within the earth and other travel along the surface.

• Waves traveling within the earth are known as body waves. There are two types of body waves:

– primary waves (P)

• compressional; propogate through all materials; fastest

– secondary waves (S)

• shear waves; only travel through solids

Primary (P) Waves

Secondary (S) 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.

Potential Shaking in LA Area (figure)

Potential Shaking in LA Area (figure)

Potential Shaking in LA Area (figure)

Potential Shaking in LA Area (figure)

Measuring Earthquakes

• seismograph: records the vibrations of the crust

• Richter Scale measures
vibration, 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 magnitude
Destroyed Glendale College Buildings!

• San Fernando, 1971 - 6.6

• Northridge, 1994 - 6.7

• Hector Mine, 1999 - 7.1

San Francisco, 1906
Magnitude: 7.9

San Fernando, 1971 (6.7)

Northridge, 1994 (6.7)

Northridge, 1994 (6.7)

Northridge, 1994 (6.7)

Denudation

• Once the mountains have been built, how are they worn down, back to the see?

• Process called denudation

• Weathering is the term applied to all processes that break down rock into smaller rocks (sand, silt, etc.)

Outcrops and Alluvium

• Outcrops are spots on the land where the parent bedrock is visible at the surface.

• Alluvium is the sediment, or weathered rock material that has been transported and deposited by a stream (also called in this text transported regolith).

Physical and Chemical Weathering

• Involves the breakdown of rock into smaller pieces by the mechanical action of wind, rain, water and ice.

• Salt Crystalization can also break apart rock in dry climates.

• Common at the bottom of hills and mountains where water is more plentiful

• Some rocks (e.g. limestone) break down by chemical processes.

Bedrock Disintegration (fig).

Joint Block Separation (fig.)

Joint Block Separation (fig.)

Joint block disintegration Granite (fig.)

Salt Crystallization (fig.)

Oxidized Rock (figure)

Hydrolysis (fig.)

Chemically Weathered Granite (fig.)

Chemically Weathered Granite (fig.)

Carbonic Action (fig.)

Weathered tombstones (fig.)

Carbonic Action (fig.)

Carbonic Action (fig.)

Solution Pitting of Limestone (fig.)

• May also have salt crystal mechanical weathering as well.

Mass Wasting

• Mass wasting is the spontaneous downhill movement of rock, soil and regolith.

• It comes in many forms, but is generally classified by the rock/soil type and the speed of downward motion.

• The common characteristic is that it is all generated by the force of gravity.

Mass Wasting

Types of mass wasting (fig)

Soil Creep (fig.)

Slump (fig.)

Induced Mass Wasting

• Humans are often responsible for creating conditions that favor mass wasting.

• Building houses on steep slopes, clear-cutting and forest fires can all create ideal conditions for mass wasting.

• Association with Wildfires

• The PCH was cut off at Malibu in the early 1990s.

Induced Earthflows

• Often occurs on land that overlies a shale and clay bedrock formation.

• Water, either from heavy rains or from human sources can make the bedrock slide downward on the clay once the clay is made more plastic and slippery by excess water.

Subsidence

Subsidence is the process of sinking land

Can be caused by a number of factors, but in California, pumping underground water out too fast can be a cause.

Fluvial Geomorphology

• This section is about the ways in which flowing water erodes the land and how that flowing water also creates landforms.

• Along with wind, ice and waves, running water is a process of denudation, or the wearing away of landforms.

Fluvial Processes and Landforms

• Fluvial (of or pertaining to running water) processes create fluvial landforms.

• Fluvial landforms can be found in virtually all parts of the globe.

• Fluvial processes may not be the most powerful, but they are the most important and over time, the most effective.

Erosional and Depositional Landforms

• There are two types of fluvial landforms: those carved out by fluvial processes (erosional) and those created, or built by fluvial processes (depositional).

• Valleys are erosional features and floodplains and sandbars are depositional features.

Erosional and Depositional landforms (fig.)

Rainsplash (fig)

Rills (fig.)

Shoestring Rills (fig.)

Gullied Pasture (fig.)

Gully Form (fig.)

Erosion

• Erosion is the most degrading force upon soil.

• Soil always goes some place else.

• Sometimes it can be captured and reused, but if it makes it to the ocean, it is lost to all.

• $44 billion dollars (US) $400 billion lost directly and indirectly per year because of soil erosion.

Erosion Factors

• Vegetative Cover

• Slope

• Rainfall (intensity and volume)

• Soil type

• Land management

Consequences of Erosion

• Lower yields, higher fertilizer use, more expensive food.

• Loss of arable lands, fragmentation of agricultural areas, higher food costs and ecosystem fragmentation.

• Sedimentation of various wetland areas which upsets the habitat of these ecologically sensitive areas.

• Increases the dirt in water (increases turbidity), which upsets the stream habitats.

• Flooding!

Agricultural Topsoil Loss (fig.)

Topsoil Loss (fig.)

Erosion (fig.)

Colluvium and Alluvium

• At the base of hills where erosion is occurring a pile of eroded materials may accumulate, called colluvium.

• If the material is transported away from its source by water, then it is called alluvium.

• Alluvium is generally a good thing for agriculture, but too much can ruin farming.

• Too much alluvium can also increase floods.

Arid Climate Erosion

• Where rainfall is scarce, so is the vegetative cover. Where normal conditions prevail, erosion can be sustained and it may not be damaging.

• Dry climates are however far more susceptible to hard rains or changes in land use.

• Badlands can develop in areas where erosion exceeds the natural capability of a region to build or rebuild soil.

• Human activity can create badland conditions, like it has on shortgrass prairie in the upper plains.

Badlands (fig.)

Badlands (fig.)

Badlands (fig.)

Badlands (fig.)

Stream Processes

• Consists of three activities:

• Erosion

• Transportation

• Deposition

Stream Erosion

• There are a number of ways a stream can erode a soil or rock formation.

• Corrosion occurs from chemical weathering (lmst)

• Generally water contains particles which act like sandpaper and/or a jackhammer on contact surfaces. This process is known as hydraulic action.

• Those rocks dragged along the bottom of the stream are abraded and broken down.

• Rock pieces that get stuck in a single spot can create a pothole.

Potholes (fig.)

Potholes (fig.)

Pothole (fig.)

Potholes (fig.)

Stream Transportation (fig.)

• All the solid materials that are carried by a stream is its load.

• Some of it is dissolved in solution, making it invisible to the naked eye.

• A much larger portion is carried in suspension, mostly clay and silt (muddiness)

• Some of it is dragged along the bottom as bed load. Most of this is sand and gravel.

• The majority of stream load is in suspension.

Bed Load (fig.)

Stream Load Capacity

• How much a stream carries can be measured against how much could carry.

• The load potential of a stream is largely a factor of stream velocity and the resultant turbidity.

• When stream velocity is doubled, load capacity can increase exponentially.

• The vast majority of erosion during a year will occur during the infrequent high water moments.

Stream Gradation

• The steeper the grade, the greater the velocity of the stream and the greater the erosive capacity of the stream.

• Streams erode into the soil and rock they overlie. Once they have flattened out they are called graded streams.

• Stream flowing over newly uplifted ground have many knickpoints or waterfalls.

Stream Gradation (Fig.)

Landscape Evolution

• Landscapes being eroded by streams go through a sort of life cycle.

• New or young fluvial landscapes are characterized by lots of waterfalls, rapids and lakes.

• Eventually the waterfalls are eroded into gorges/canyons and the lakes are filled with sediment.

• Very little sediment is otherwise deposited by the system.

Landscape Evolution

• The stream “tries” to create a condition where the slope of the stream (gradient) is constant throughout the entire stream.

• The tributaries extend into highland areas, eroding them and creating ever-extensive watersheds.

• Once a graded condition has been achieved, then the ability of the stream to carry load will be matched by the available load. Deposition will begin to take place.

Floodplain Creation

• Slow flowing, well graded streams cannot carry all the sediment fed to them, so they begin dropping it off in widening valleys.

• Within these floodplains, rivers will begin to meander, cutting banks on the outside corners of the stream and depositing sediment in point bars.

• The edges of the gorges will evolve into valley walls that are less steep.

Meanders (fig.)

Floodplain Features

• Among those features common in a mature stream floodplain are:

• Meanders

• Cutbanks

• Point bars

• Oxbow Lakes

• Natural levees

• Backswamps and bluffs

Floodplain features (Fig.)

Valley Evolution (fig.)

Waterfalls

• Some are created by rifting, like in E.Africa

• Others, like Niagara, were created by the movement of great glaciers in the region and by differential erosion patterns of layers of bedrock (shale vs. limestone)

• Where in California?

• Where waterfalls exist, so does hydroelectric power potential. Where graded stream conditions are present, dams are necessary precondition of hydropower production.

• Pros and Cons of dam construction.

Waterfall (fig.)

Waterfall (fig.)

Waterfall (fig.)

Braided Stream (fig.)

Natural Bridge (fig.)

Natural Bridge (fig.)

Gooseneck (fig.)

Rejuvenation (fig.)

Alluvial Rivers

• Alluvial rivers are those flowing through alluvial floodplains created by the river itself.

• They are prone to frequently flood events.

• Natural levees are produced by the floods.

• The bluffs are above the floodplain.

• Alluvial rivers often meander enough that they cutoff their own course creating oxbow lakes and later meander scars.

Alluvial River (fig.)

Alluvial River (fig.)

Alluvial River (fig.)

Alluvial River (fig.)

Rivers in Deserts

• Although it may rain rarely in deserts, because the vegetation is sparse, rain events have a heightened erosional impact.

• Flooding in desert environments can be extremely rapid and dangerous.

• Because seepage is so increased in dry regions with deep water tables, streams tend to dry up quickly and remain shallow and frequently braided.

Desert Flash Flood (fig.)

Alluvial Fans

• Alluvial fans are common desert landforms that are built of sediments eroded from highland areas.

• They are cone shaped with the small point emanating from the mouth of a ravine between two high points.

• Alluvial fans serve as important aquifers in dry/moutainous climates because the sandy lower layers capture and hold much water.

Alluvial Fan Cross-section (fig.)

Alluvial Fan (fig.)

Glacial Geomorphology

• http://www.uwsp.edu/geo/faculty/lemke/alpine_glacial_glossary/index.html#contents

• A very nice web site with lots of pictures and maps.

Glaciers in California

• Much of the mountainous region in the Northern part of the state has glacial landscapes.

• Most of the glaciers are now melted, but several smaller ones exist in places.

• Where are the likely locations?

Glacial Landforms

• Yosemite is famous for its stunning glacial landscapes.

• Below are graphics that illustrate the various features, including:

• U shaped valleys

• Cirque, Hanging Valleys, Waterfalls

• Moraines (lateral, terminal)

• Horns, Aretes

Glacial Landforms (fig)

Arete (fig)

Horn (fig)

Horn (fig)

Cirque (fig)

U Shaped Valley (fig)

Hanging Valley (fig)

Hanging Valley 2(fig)

Moraine (fig)

Topo Map: Mt. Abbot’s Glacial Landforms (fig)