1300 Chapter 3 - Earth Science Tradition

Physical Geography

• Concerns itself with the study of the Earth itself and the various processes which shape and change the world on and in which we live.
• A study of landforms and how they are changed and created.
• Creation Forces – push, move, and raise
• Erosional Forces – scour, wash, and wear down

Geomorphology

• the study of the origin, characteristics, and development of landforms. Geomorphologists study erosion, transportation, and deposition of materials and inter-relationships between climate, soils, plants and animals, and landforms.

Earth Materials

• The earth is made of rocks and their erosional remains.

Minerals

• Consist of a specific chemical combination with a specific hardness, density, and structure.
• Igneous Rocks – created from cooled molten rock
• Intrusive Igneous Rocks – formed below ground level by magma
• quartz, granite
• Extrusive Igneous Rocks – formed above ground from lava
• basalt, obsidian
• Sedimentary Rocks – created from material eroded from existing rock and deposited through the actions of water (and wind) and then compressed over time.
• Strata – the layers of sedimentation
• Sedimentary rocks generally indicate that the region was once under water, a part of a sea or lake.
• Conglomerate Forms – large and rounded particles
• Sandstone – sand particles
• Shale or Siltstone – from silt and clay
• Limestone – from marine coral, shells and skeletons
• Bituminous Coal – mainly from vegetation
• Petroleum – from organic material which undergoes a chemical process
• Gas and oil are lighter then the materials around them and so rise upward until blocked by an impermeable layer of rock.
• The White Cliffs of Dover are an example – dolomite
• Metamorphic Rocks – (“changed shape”) formed from igneous and sedimentary rocks through heat, pressure, or chemical reactions.
• Shale becomes Slate
• Limestone becomes Marble
• Granite becomes Gneiss
• Some metamorphic rocks are the Earth’s oldest known rocks.

Geologic Time

• The earth is 4.7 Billion years old! The study of the physical earth involves great time depth and long periods of formation and destruction.
• punctuated equilibrium…

Plate Tectonics

• explains Continental Drift
• Continents began in Pangaea and then moved to their current positions
• Early 20th century work by geologist Alfred Wegener on continental drift helped to explain how landforms developed over time
• The movement is driven by convection currents in the earth’s mantle and core.
• Divergent – new crust forming – mid-ocean rides
• Convergent – coming together – subduction zone
• Transform – moving past one another

Plate Tectonics Continued

• Asthenosphere – the partially molten layer immediately below the Lithosphere
• Lithosphere – the thin shell of rocks that forms the Earth’s crust.
• 12 large and several smaller plates
• Continental and Oceanic Crust
• Faults – fractures in the rocks along which there is movement.
• These occur at plate boundaries and within plates
• Subduction Zones
• Areas where two plates meet and one is being pushed under the other.
• Hot Spots
• Areas within a plate where the plate has broken or fractured and allowed a plume of magma to rise toward the surface

Tectonic Forces

• Responsible for the building up and creation of land

Diastrophism

• The pressure acting on the plates to fold, twist, warp, and break them.

Volcanism

• the transportation of magma toward or to the surface of the earth.

Diastrophism

• Broad Warping – may be up or down warping where the earth is compressed by the weight of the continent.
• Folding – a warp or bend where the lithosphere is thrust upwards
• Faulting – a break or fracture in the rock along which movement has taken place. Movement may result in uplift and/or down-thrust
• Escarpment – formed by uplift or down-thrust on one side of the fault
• Rift Valley – formed either when one side of a fault is pushed over another or when the fault’s sides pull away from each other
• Joints – a fault with little movement.

Volcanism

• Strato or Composite Volcano – when volcanic material is expelled explosively onto the earth’s surface – forming a steep-sided cone composed of alternate layers of lava, ash, and cinders.
• Shield Volcano – an eruption without explosions forming a gently sloping volcano.

Gradational Processes

• Responsible for the reduction of land surface

Weathering

• the breakdown of rocks and minerals at or near the earth’s surface by atmospheric factors
• Mechanical Weathering – the physical disintegration of earth materials
• Frost action
• Formation of salt crystals
• Root action
• Chemical Weathering – the decomposition of minerals due to chemical reaction
• Oxidation – formation of oxides (rusting)
• Hydrolysis – caused by water
• Carbonation – caused by acids

Mass Movement

• Downslope movement of material due to gravity (also called mass wasting)
• Avalanches
• Landslides
• soil-creep
• mud flow
• formation of talus slopes

Erosional Agents and Deposition

• Running Water – the most important erosional agent
• The amount of precipitation
• The length and steepness of the slope
• The kind of rock and vegetative cover
• Abrasion
• when the particles contained within the running water wear away at the surrounding surfaces.
• Load
• the amount of material suspended within the water, dependent upon water velocity.
• Load Deposition may form deltas and rich or poor bottom land.

Stream Landscapes

• In Humid Areas
• falls – flow over precipices
• V-shaped channels – formed in steep downhill gradients
• Floodplains – broad, flat valleys formed in low to moderate gradients
• Meanders – the path of a stream across a floodplain
• Oxbow Lakes – old meander channels
• Natural Levees – formed in floodplains by the deposition of silt along the path of the stream/river
• In Arid Areas
• Playas – temporary/seasonal lakes
• Alluvium – sand and mud buildup in lakes
• Alluvial Fans – formed along hillsides
• Arroyos – deep, straight-sided canyons
• Wash – channels within an alluvial fan
• Buttes and Mesas – erosional features of arid water erosion

Groundwater

• Water that has sunk underground into the soil and rocks
• Aquifer – zone of saturation (accumulated groundwater)
• Water Table – the upper level of an aquifer
• Solution – chemical erosion of material by groundwater along with carbon dioxide
• Karst Topography – limestone region marked by sinkholes, caverns, and underground streams.

Glaciers

• A large body of frozen water moving slowly down a slope or spreading outward on a land surface.

• Glacial Trough – a deep U-shaped valley formed by the glacier’s movement
• Fiord – a glacial trough below sea level
• Cirques – small depressions formed by ice erosion at the head of a glacial valley
• Tarn – small lakes formed in the cirques
• Till – deposits of debris left at the head of a glacier or along its path as it melts
• Outwash plain – a gently sloping area formed by water from a melting glacier

Permafrost

• A permanently frozen layer of ground

Waves, Current, and Coastal Landforms

• Constant and unceasing erosional action.
• Longshore Currents – move parallel to the shore and transport sand
• Beaches – depositions of sand along a sloping shore
• Spits - A small point of land running into the sea, or a long, narrow shoal extending from the shore into the sea
• Sandbars – depositions of sand away from the shoreline, where no longshore current exists
• Lagoons - body of comparatively shallow salt or brackish water separated from the deeper sea by a shallow or exposed sandbank, coral reef, or similar feature.
• Inlets - an indentation of a shoreline, usually long and narrow; small bay or arm
• Salt Marches - a type of marsh that is a transitional zone between land and salty or brackish water (e.g., sloughs, bays, estuaries).
• Coral Reefs – formed by the coral organisms found throughout the world
• Atolls – coral reefs formed in shallow water around a volcano that has since been covered or nearly covered by water.

Wind

• Major erosional and depositional force where soil is exposed.
• Gravelly Deserts
• Sandy Deserts
• Dunes – from sand, created by wind
• Barchan – crescent shaped dune
• Loess – silty soil usually found in the mid-latitudes, usually very rich