Chapter 3 Land

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