Chapter 16 Earth’s Surface Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Interpreting Earth’s surface Principle of uniformity (James Hutton) “The present is the key to the past.” Rocks are changed today by the same processes that changed them in the past Replaced catastrophic models of previous thinkers Catastrophic events contribute nonetheless Volcanoes, earthquakes, meteorite impacts, …

Diastrophism Any process of deformation that changes the Earth’s surface Produces structures such as plateaus, mountains and folds in the crust Related to volcanism (the movement of magma) and earthquakes Basic working theory is plate tectonics

Stress and deformation Possible material responses to stress No change Elastic change with recovery Plastic change with no recovery Breaking from the pressure

Stress and deformation Cont. Rock variables Nature of the rock Temperature of the rock Speed of stress application Confining pressure Interplay between these variables produces observed rock structures

Folding Sedimentary rocks Originate from flat sediment deposits Layers usually horizontal Folds Bends in layered bedrock Result of stress produced plastic strain Widespread horizontal stress can produce domes and basins

Domes

Basins

Faulting Fault Produced by relative movement on opposite sides of a crack Footwall: mass of rock below the fault Hanging wall: mass of rock above the fault Fault plane: surface between the footwall and hanging wall

Faulting Cont. Shows how the hanging wall has moved relative to the footwall. Hanging wall is on the left Footwall to the right

Three Classes of Faults 1. Normal fault Hanging wall has moved down relative to the footwall Related features Graben Block surrounded by normal faults drops down Horst Block surrounded by normal faults is uplifted

Other Faults 2. Reverse fault 3. Thrust fault Hanging wall moved upward relative to footwall Result of horizontal compressive stress 3. Thrust fault Reverse fault with a low-angle fault plane Faults provide information on the stresses producing the formation

Earthquakes Quaking, shaking, vibrating or upheaval of the ground Result from sudden release of energy from stress on rocks Vibrations are seismic waves Most occur along fault planes when one side is displaced with respect to the other

Causes of earthquakes Elastic rebound theory Two plates press tightly together Friction restricts motion

Causes of earthquakes Cont. Stress builds until friction or rock rupture strength is overcome Stressed rock snaps suddenly into new position

Locating and measuring earthquakes Focus Actual origin of seismic waves Epicenter Location on Earth’s surface directly above the focus Locating and measuring earthquakes

Locating and measuring earthquakes Seismometer Instrument used to detect and measure earthquakes Detects three kinds of waves P-wave (longitudinal) S-wave (transverse) Surface wave (up and down)

Seismic data P-waves travel faster than S-waves Difference in arrival times correlates to distance from earthquake Triangulation used to pinpoint epicenter and focus

Earthquake Magnitude Effects: structural damage to buildings, fires, landslides, displacement of land surfaces, tsunami (tidal wave) Richter scale Based on swings in seismograph recordings Logarithmic scale Number increases with magnitude of the quake 3(not felt); 9(largest)

Anchorage, March 1964 (9.2)

Northridge, January 1994 (6.7)

Oakland, October 1989 (6.9)

Tsunomi Very large ocean waves Generated by strong disturbance in ocean floor Earthquake, landslide, volcanic explosion Speeds of up to 725 km/h (459 mi/h) Wave height can be over 8 m (25 ft) Very long wavelength of up to 200 km (120 mi)

Indian Ocean Tsunami

Before and After

Before and After

WARNING: GRAPHIC PICTURE

After Tsunami

Origin of mountains Mountains Elevated parts of Earth’s crust rising abruptly above the surrounding surface Created by folding and faulting of crust Three basic origins Folding Faulting Volcanic activity

Folded and faulted mountains Domed mountains Broad arching fold Overlying sedimentary rocks weather away, leaving more resistant granite peaks

Folded and faulted mountains Cont. Fault block mountains Rise sharply along steeply inclined fault planes Weathering erodes sharp edges

Volcanic mountains Volcano A hill or mountain formed by the extrusions of lava or rock fragments from magma below Structure: vent, crater, lava flow

Mt. St. Helens

May 18, 1980

Eruption!

Ash Clouds

Before and After

Before and After

Spirit Lake Before

Spirit Lake After

Spirit Lake – 2006

Mt Adams from Mt. St Helens showing tree damage

Edge of Blast

Growing Lava Dome

Growing Lava Dome

Hot Spots Thermal blooms Maybe up to 2000 miles deep Plate moves over hot spot Islands develop over time---depends how long in one area

Volcanic Hot Spots

Shield Volcano

Processes That Tear Down Slow changes resulting in the breakup, crumbling and other destruction of solid rock Includes physical, chemical and biological processes Contributes to The rock cycle Formation of soils Movement of rock materials over Earth’s surface

Mechanical weathering Erosion: The process of physically removing weathered materials The physical breakup of rocks without chemical change Disintegration processes Wedging By frost By trees

Chemical weathering Decomposition of minerals by chemical reactions Oxidation Reactions with oxygen Produces red iron oxides

Chemical weathering Cont. 2. Carbonation Reactions with carbonic acid (carbon dioxide dissolved in water) Easily dissolves limestone 3. Hydration Reactions with water Includes dissolving in water and combining with water

Erosion Mass movement Erosion caused directly by gravity Creep The slow movement of soil down a steep slope Landslide Any slow to rapid downhill movement of materials

Running water Streambed transport: Dissolved materials Suspended materials Rolling, bouncing and sliding along stream bed Streambed evolves over time

Streams Youth Landmass recently uplifted Steep gradient, V-shaped valley w/o floodplain Boulders, rapids and waterfalls Maturity Stream gradient smoothed and lowered Meanders over floodplain Old age Very low gradient Broad, gently sloping valleys Sluggish flow; more floods

Stream development Cont. Three stages in the aging and development of a stream (A) Youth (B) maturity (C) old age

Deltas Deposits of sediment at the mouth of a river or stream Stream flow dissipates into an ocean or lake Erosive and sediment-carrying abilities lost

Glaciers Masses of ice on land that move under their own weight Form from snow accumulated over a number of years

Glaciers Cont. Alpine glaciers Form at high elevations Flow through valleys Also “valley glaciers” Continental glaciers Cover large area of a continent Today in Greenland and Antarctica

Tracy Arm, Alaska

Glacier erosion Glaciers: Three mechanisms: Bulldozing Forms deposits called moraines Abrasion Produces powdery, silt-sized rock flour Plucking Glacier water freezes into surrounding rock and pulls it along

Wind Considerably less efficient than water or ice Two major processes Abrasion Natural sandblasting Produces ventifacts Shape can depend on prevailing winds Deflation Loose material picked up and carried away by the wind

Wind Cont. Wind-blown deposits Dunes: low mound or ridge of sand or other sediment Loess: fine dust deposited over a large area

Death Valley

Indiana Dunes

Great Sand Dunes

Loess Hills Scenic Byway

Loess Hills