CHAPTER 3 Landforms
Sep 01, 2014
CHAPTER 3 Landforms
Study of the landforms and the processes that create them
Geomorphology
Important Points Study of the Lithosphere Elements of surface have identifiable
forms are called landforms Mountains Plains Plateaus Valleys
Landforms constantly change Geographers study topography (shape of
the earth’s surface)
Processes that create landforms
Endogenic Processes Internal Forces Earthquakes Volcanoes
Exogenic Processes External
Forces Erosion Weathering
Plate Tectonics
Alfred Wegener
Theorized in 1912; proven after WWII
12 large tectonic plates float on the mantle
200 million years ago, all one continent (Pangaea)
http://www.classzone.com/books/earth_science/terc/content/visualizations/es0807/es0807page01.cfm?chapter_no=visualization
Ring of Fire
Types of Boundaries Divergent boundaries
Spread Apart Generally mid-ocean; causes sea floor spreading Underwater volcanoes, few quakes
Convergent boundaries Push together Usually near continental edges Violent volcanoes near ocean, strong quakes
Transform boundaries Grind together No volcanoes, mild to strong quakes (San
Andreas)http://www.learner.org/interactives/dynamicearth/plate.html
Earthquakes Crust movement where
plates meet 500,000 per year; 800 felt Seismic waves of energy
(vibrations) Seismograph measures
waves Earthquakes don't kill people,
buildings (and gas mains) do Epicenter – point on the surface directly above the focus of an earthquake
Bam, Iran 12/26/2003
San Andreas“San Francisco”
M8.5 – April 18, 1906, 3,000 deaths
$400 million in damage
Rock Formation Types
Igneous – molten rock cools; basalt Sedimentary – rocks eroded from
mountains; shale Metamorphic – exposed to heat/pressure
and compressed; marble & slate Minerals (specific chemical compounds)
Sima – Dense w/silicon & magnesium; ocean floor
Sial – Less dense w/silicon & aluminum; makes up crust
Stress on Rocks Fault - a break in
Earth’s crust where slabs of crust slip past each other.
They usually occur along plate boundaries where the forces of plate motion compress, pull, or shear the crust so much that the crust breaks.
Normal fault The fault is at an
angle, so one block of rock lies above the fault while the other block lies below the fault.
Found near a divergent plate boundary
Reverse Faults Compression
produces reverse faults.
It is like a normal fault but the blocks move in the opposite direction.
Near convergent boundaries
Reverse Fault - Appalachian Mountains
Strike-slip fault Strike-slip fault -
shearing causes these faults. Rocks on either side of the fault slip past each other sideways with little up-or-down motion. They also form transform boundaries.
Example - San Andreas fault
Mountain Building Over millions of years,
fault movement can change a flat plain into a towering mountain range.
Mountains Formed by Faulting When normal faults uplift a block of rock, a fault-block mountain forms.
Teton Range near Wyoming and Idaho was formed this way.
Mountains Formed by Folding Have you ever skidded on a rug that
wrinkled up as your feet pushed it across the floor?
Folds - bends in rock that form when compression shortens and thickens part of Earth’s crust.
Mountains caused by Folding
Himalayas Alps
Volcanoes Pressure on molten rock Shield volcanoes
Made of basalt More calm and constant (runny lava) Along divergent boundaries or at hot
spots Relatively less dangerous
Composite volcanoes Violent and explosive (lava & ash) About 600 active (1000s dormant) Relatively hard to predict Can cause major climate changes
Mauna Loa Shield Volcano
Mt. St. Helens 5/18/1980Composite cone volcano
Exogenic ForcesReshape the Earth’s crust into new landforms
Weathering Process of breaking down rocks into pieces First step in the formation of soil Most mountains are going down faster than
they’re going up Mechanical weathering breaks rocks into
smaller pieces Frost action Salt crystals Roots Exfoliation
Rock chemistry does not change
Frost Action
Weathering Chemical weathering changes the
chemistry of rocks Oxidation (exposure to oxygen) Hydrolysis (exposure to water) Carbonation (exposure to carbon dioxide)
Warmth and water encourage chemical reactions
Weathering loosens rock particles, creates soil
Oxidation
Carbonation: KarstFormed by the dissolution of soluble rocksKarst regions contain aquifers that are capable of providing large supplies of water.
Erosion & Deposition Erosion carries particles away Surface Erosion – water carrying particles
Rainfall Relatively slow
Running water Constant water, floods Most important landform agent in deserts Floodplains, levees, and deltas
Deposition deposits them
Streams are vital geologic agents
Carry most of the water that goes from land to sea (groundwater & overland flow)
Transport billions of tons of sediment to the ocean each year
Transport billions of tons of soluble salts to the oceans each year
Shape the surface of the Earth
Stream Flow
Some of the consequences of natural stream flow present engineering and social challenges with which
we grapple year after year, and have through civilization’s history.
The flow of fresh water in channels on the Earth’s surface has been essential to the development of
topography and most ecosystems.
Floodplain
Delta
Levee
flat or nearly flat land adjacent to a stream or river that experiences occasional or periodic flooding
deposit at the mouth of a river is usually roughly triangular in
shape
river's banks are built up above the level of the rest of the floodplain
Meander
These are satellite images before and during Summer, 1993 floods of the Mississippi river north of St.Louis.
Mississippi Floodplain
Alluvial fan fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads
Streams Locked in Valleys
Streams like these (and the Potomac River at Great Falls) have virtually no (normal) floodplains. They have carved into rock so deeply, that their meandering and other
characteristic evolutionary features are restricted.
Glaciers
Rivers of ice Types
Alpine Glaciers – snow accumulation over years
Continental Glaciers – covers vast areas Carve out landforms from mountains Deposit material when they leave
Moraines Outwash plain
Past 200 years has seen glacial shrinking
Glacial landforms
Outwash Plain- large volumes of rock and dirt debris that often spreads out in a great sheet
Terminal Moraine - accumulation of boulders, stones, or other debris carried and deposited by a glacier
Alaska
Long Island, NY
Glacial landforms: California
Glacial landforms: Iowa
Iowa is almost entirely covered by loose sediments left behind by the continental glaciers which has created fertile soil
Waves and coastlines
Waves transfer energy through wind Energy moves particles down the coast
(longshore current) Newer coastline=erosion Older coastline=deposition Tsunami – extremely long wave created
by earthquake Barrier reef: only organically formed
landformhttp://www.uky.edu/AS/Geology/howell/goodies/elearning/module14swf.swf
Longshore current
Pacific Palisades
Longshore currents affect shorelines by redistributing sand and sedimentalong their path.
Erosion vs. deposition
Acapulco
Cancún
Great Barrier Reef