Shaping Earth’s Surface

Weathering, Erosion, and Transportation

The Earth is constantly undergoing gradual changes The Earth is moved by weathering, erosion, and then transported to different areas on the Earth.

Weathering

Importance of Weathering –Participates in the rock cycle –Used in the formation of soils –Helps in the movement of rock material over the Earth’s surface.

Erosion –Weathering breaks the rocks into fragments –Erosion then transports the material to new places of the Earth –This is the physical process of removing the weathered material.

Transportation –The movement of eroded materials by rivers, glaciers, wind, or waves. –As material is transported the weathering and erosion process continues

This famous natural bridge is an example of a landform created by the sculpturing power of weathering and erosion. It is Rainbow Bridge in the Rainbow Bridge National Monument, Utah.

The piles of rocks and rock fragments around a mass of solid rock is evidence that the solid rock is slowly crumbling away. This solid rock that is crumbling to rock fragments is in the Grand Canyon, Arizona.

Mechanical Weathering –The physical breaking of rock material without any change to their chemical composition –Exfoliation Spalling off layers of rock Caused by reduced pressure on rocks as material is removed from above. –Frost wedging Caused as pores or cracks become filled with water and then freeze and thaw. As the process repeats cracks and pores become larger Eventually the rock will break off.

(A)Frost wedging and (B) exfoliation are two examples of mechanical weathering, or disintegration, of solid rock.

Growing trees can break, separate, and move solid rock. (A) Note how this tree has raised the sidewalk. (B) This tree is surviving by growing roots into tiny joints and cracks, which become larger as the tree grows.

Spheroidal weathering of granite. The edges and corners of an angular rock are attacked by weathering from more than one side and retreat faster than flat rock faces. The result is rounded granite boulders, which often shed partially weathered minerals in onion-like layers.

Chemical Weathering –The alteration of materials by chemical reactions which do change the chemical composition of the material. –Oxidation When oxygen reacts with minerals in rocks –Carbonation A reaction between carbonic acid and minerals in rocks –Hydration A reaction between water and the minerals in rocks. Dissolves material Water combines with the mineral to form a hydrate

Limestone caves develop when slightly acidic groundwater dissolves limestone along joints and bedding planes, carrying away rock components in solution. (A) Joints and bedding planes in a limestone bluff. (B) This stream has carried away less-resistant rock components, forming a cave under the ledge.

Soils

–Soil is a mixture of unconsolidated weathered Earth materials and humus Humus –Decayed organic matter Bedrock –Solid rock below the soil Loam –A soil that is a mixture of sand, silt, and clay –Also referred to as topsoil

Erosion

Mass Movement –Criteria Material –bedrock that has been weathered and eroded –debris that is carried away during the mass movement. Rate –The speed at which the movement occurs Type –Fall –Slip »Slump »Slide –Flow

–Creep The slow downhill movement of soil down a steep slope –Fall material moves in free fall down a cliff –Slip - materials moving together along a surface Slump - Movement along a curved surface Slide - Movement along a plane parallel to the surface. –Flow – Mass movement of a liquid

The slow creep of soil is evidenced by the strange growth pattern of these trees.

Running Water –Stream Channels Move materials in 3 ways. –As dissolved material in a solution –As materials carried in suspension –As sand and larger materials rolled, bounced, and slid along with a stream Most of the erosion that a stream does is done by the larger material that moves along with it on the stream bed.

Moving streams of water carry away dissolved materials and sediments as they slowly erode the land.

–Stream Erosion and Deposit Features Floodplain –The wide, level floor of the valley adjacent to a stream that has been built by the stream over time. –This is the area that the stream will begin to move into when moisture is high (flood). –A young stream usually has a v shaped flood plain whereas a mature stream has a flattened floodplain. Delta –Where the stream empties into an ocean or a lake it loses all of its sediment carrying ability –The sediments are deposited at the mouth of the stream and form a deposit

A river usually stays in its channel, but during a flood it spills over and onto the adjacent flat land called the floodplain.

Three stages in the aging and development of a stream valley, (A) youth, (B) maturity, and (C) old age.

The waterfall and rapids on the Yellowstone River in Wyoming indicate that the river is actively down cutting. Note the V-shaped cross-profile and lack of floodplain, characteristics of a young stream valley.

(A)Delta of Nooksack River, Washington. Note the sediment-laden water, and how the land is being built outward by river sedimentation. (B) Cross section showing how a small delta might form. Large deltas are more complicated than this.

Glaciers – A mass of ice on land that moves under its own weight. –Origin of Glaciers As snow melts and refreezes it is turned into ice. After years of repeated thawing of snow and refreezing into ice, the weight above begins to pack down the ice below. The increased pressure drives out air and reforms the ice into a crystalline structure of interlocking ice crystals with a very high mass Alpine glaciers form in high elevations Valley glaciers form and flow downhill through a valley Continental glaciers cover large areas of a continent.

Valley glacier on Mount Logan, Yukon Territory.

–Glacial Erosion and Deposition A glacier erodes material by: –Bulldozing –Abrasion –Plucking Material; that is deposited by a glacier forms a moraine Plucking material produces a depression called a cirque As abrasion continues material becomes ground into fine sediment called rock flour.

(A)A stream-carved mountainside before glaciation. (B) The same area after glaciation, with some of the main features of mountain glaciation labeled.

Wind –Wind Erosion and Transportation Wind abrasion is the sandblasting process that occurs as material is carried along with wind. Deflation is the picking up of loose materials from the Earth’s surface. –Wind Deposits Dunes –A low mound or ridge of material sediments –Form where the wind that is carrying the sediment encounters some obstruction Loess –Very fine dust or silt that is deposited over large areas. –The source of the material is thought to be rock flour from glacier action

Ventifact formation by abrasion from one or several directions.

Development of Landscapes

Rock Structure –Type of rock igneous metamorphic Sedimentary –If they have been disturbed by faulting or folding

Weathering and Erosion Process –Controlled by climate and elevation State of Development –How effectively the landscape has been attacked by erosion processes

This melting glacier (A) is the source for a stream (B) that flows through a valley in the youth stage.