Overview Earth Materials Geologic Time Movements of the

Continents Tectonic Forces Gradational Processes Landform Regions

Earth Materials Igneous Rocks Sedimentary Rocks Metamorphic Rocks

Igneous Rocks Formed by the cooling and solidification of

molten rock Magma: molten rock below ground

Cooling forms intrusive igneous rocks Granite

Lava: molten rock above ground Cooling forms extrusive igneous rocks

Basalt, pumice, obsidian Composition of magma and lava plus cooling

rate determines the minerals that form

Sedimentary Rocks Composed of eroded particles of gravel, sand,

silt, and clay Rocks evolve in horizontal strata

Compressed by weight of additional deposits and cemented by water and certain minerals

Type of sediment determines rock type Large, rounded particles form conglomerates Sand forms sandstone Silt and clay form shale or siltstone Organic materials form limestone or coal

Metamorphic Rocks Formed from igneous or sedimentary rocks by

earth forces that produce heat, pressure, or chemical reactions Mineral structure is changed

Shale becomes slate Limestone may become marble Granite may become gneiss

Geologic Time Earth formed about 4.7 billion years ago Theory of continental drift

Based on early 20th-century work of Alfred Wegener All land masses were once united in a supercontinent;

continents drifted apart over many millions of years Pangaea: “all Earth”

Forerunner of plate tectonics theory

Movements of the Continents Plate tectonics theory

Asthenosphere Partially molten layer above the core and lower mantle

Lithosphere Outermost layer of the earth (the crust and upper mantle) 12 large and numerous small plates that slide or drift slowly

over the asthenosphere May be due to convection of molten material in asthenosphere

Movements of the Continents Divergent plate boundaries

Plates move away from each other Transform boundaries

One plate slides horizontally past another Convergent boundaries

Plates move toward each other Subduction may occur

One plate is forced beneath another Earthquakes and volcanic activity may occur in

the vicinity of plate boundaries Ring of Fire

Tectonic Forces Diastrophism

Earth force that folds, faults, twists, compresses rock Volcanism

Earth force that transports subsurface materials to or toward the surface of the earth

Diastrophism Broad warping

Bowing of a large region of the earth’s surface Folding

Layers of rock are forced to buckle Faulting

Rock is broken or fractured Escarpments, rift valleys

Earthquake Movement along a fault or point of weakness

Tsunami Sea waves generated by an earthquake, volcanic eruption,

or underwater landslide

Volcanism Usually at or near plate intersections Also at hot spots Strato or composite volcano

Explosive, steep sides Shield volcano

Non-explosive, gently sloping Magma may not reach the surface Lava may flow through fissures or fractures

without forming a volcano

Gradational Processes Reduction of the land’s surface

Weathering Mass movement Erosion

Weathering Processes that fragment and decompose rock Mechanical

Physical disintegration Frost action Salt crystals Root action

Chemical Decomposition as a result of chemical reactions

Oxidation Hydrolysis Carbonation

Mass Movement Downslope movement of material due to gravity

Avalanches Landslides Soil creep

Talus Landform created by the accumulation of rock

particles at the base of hills and mountains

Erosional Agents and Deposition Wind, water, and glaciers

Carve, wear away, and remove rock and soil particles Material is deposited in new places

New landforms are created

Running Water Most important erosional agent Ability to erode depends upon:

Amount of precipitation Length and steepness of the slope Kind of rock and vegetation cover

Load of a stream Materials transported by a stream Decline in velocity results in deposition

Deltas: where streams meet bays, oceans, and lakes May be deposited in adjacent plains (floodplain)

Stream Landscapes Humid areas

Waterfalls V-shaped channels Floodplains Meandering streams Oxbow lakes Natural levees

Arid areas Lack of vegetation

increases erosional forces

Playas Alluvial fans Arroyos Washes Buttes and mesas

Groundwater Aquifer

Porous underground structure bearing water Water table

Upper level of the water within an aquifer Ponds, lakes, marshes, and streams form when land

surface dips below the water table

Groundwater Solution

Chemical process by which groundwater (particularly when combined with CO2) dissolves soluble materials

Significant effect on limestone Underground caverns, stalactites, stalagmites, sinkholes

Karst topography Limestone region marked by sinkholes, caverns, and

underground streams

Glaciers Huge mass of slowly moving land ice Covered a large part of the earth as recently as

10,000-15,000 years ago Form only where annual snowfall exceeds

annual snowmelt and evaporation The weight of the snow causes it to compact at the

base and form ice Ice at the bottom becomes like toothpaste and moves slowly

Glaciers Continental glaciers Mountain glaciers About 10% of the earth’s land is under ice Glaciers change landforms by erosion

Scour the land as they move Glaciers create landforms when they deposit

debris they have transported Till consists of rocks, pebbles, silt

Glacial Landforms Erosional

Glacial troughs Fiords Tarns and cirques Arêtes

Depositional Moraines Eskers Drumlins Outwash plains

Waves, Currents, and Coastal Landforms Cliffs

Formed by wave action when land at the coast is well above sea level

Beaches and spits Formed by the deposition of sand grains Longshore currents transport sand

Sandbars Formed by sand deposited by the backwash of waves May expand to enclose lagoons or inlets

Salt marshes may develop

Waves, Currents, and Coastal Landforms Coral reefs

Composed of coral organisms growing in shallow tropical water

Develop short distances offshore Atolls

Reefs formed in shallow water around a volcano that has since been covered or nearly covered by water

Wind Most significant in dry climates

Limited vegetation leaves exposed particles subject to movement by wind

Dunes Produced by wind-driven sand

Loess Deposit of windblown silt Rich soils usually form from loess deposits

Landform Regions Large section of the earth’s surface where a

great deal of homogeneity occurs among the types of landforms that characterize it Mountains Plains Plateaus