Weathering, Erosion, and Rivers Chapters 7 and 9

Weathering and Types Weathering – The process in which rocks on Earth break down and change Mechanical Weathering – Rocks break down into smaller pieces without changing chemical composition Example: I usually break boulders apart with my head for fun

Types (continued) Chemical Weathering - Rocks are broken down due to a chemical reaction in which the composition of the material changes Example – Pouring acid on my face will chemically dissolve part of my face and maybe create some new components

More Examples of Mechanical Weathering Frost Wedging – water seeps into the rock and then expands when frozen Roots – tree roots dig into bedrock splitting it open Animals – burrowing animals dig into the rock Exfoliation – rocks that were once under pressure are exposed and expand until sheets peel off Abrasion- particles bang into one another when moving

Frost Wedging

Tree Roots

Burrowing Animals

Exfoliation

Abrasion

More Examples of Chemical Weathering Water – water can dissolve minerals in rocks Oxygen – oxidation (rusting) of minerals Carbon Dioxide – combines with water in the air to form carbonic acid (weak) which reacts with calcite (creates caves)

Chemical Weathering by Oxidation

Chemical Weathering due to Acid Rain

Chemical Weathering and Cave Formation

Factors that affect the rate of Weathering Surface Area Precipitation Temperature Rock Type

Surface Area

Precipitation and Temperature

Rock Type and Composition

Erosion Erosion is the transport of rock and sediment Erosion takes place naturally 4 different ways Wind Gravity Water Ice

Wind

Gravity

Water

Ice

Soils: Result of weathering Soil is made up of weathered rock and organic material. Parent Material – the material in which soil is formed from. Residual soil - soil that has bedrock as its parent material. Transported soils – soil that has been moved from it original spot (wind, rain water, glaciers…)

Parent material……

Residual soil Soil that has bedrock underlining it.

Transported soil Soils transported from other places.

Mature Soil Profile…..

Mature Soil Profile Soil profile – cross section of any given area of land Top soil – the A horizon: gray to black, organic, sandy Sub soil – the B horizon: red or brown, clay Weathered bedrock – the C horizon: weathered parent material.

Soil Conservation……. Soil erosion – the removal of topsoil by the action of running water or wind. Reduce by: Windbreaks – belts of trees along a field Contour farming – crops are planted parallel to land contours Terraces – flattened hills and slope’s. Strip cropping – alternating crops and bare ground No-till – plowing, planting, and fertilizing are all done at the same time.

Windbreaks…..

Contour Farming……

Strip cropping…….

No – Till…….

Water Cycle

Water Cycle Definitions Precipitation – Rainfall Infiltration – Rainfall entering the ground Runoff – Water that doesn’t infiltrate and runs off the surface Evaporation – Water entering the atmosphere from bodies of water Transpiration – Water entering the atmosphere from vegetation Condensation – Water cooling into liquid from gas in the atmosphere

3 ways rivers transport sediment Suspension – small particles carried within the water Solution – minerals dissolved within the water Bed Load – large particles dragged along the bottom

Erosion by Rivers Young Rivers – deepen the valley Old Rivers – widen the valley Meanders Erosion takes place on the outsides of the meander Deposition takes place on the inside of the meander

River Stages and Development

Rivers are classified as 3 different stages Young Mature Old

Young Water moves rapidly The water cuts downward, deepening the valley Rapids, waterfalls, etc. Poor drainage Little or no flood plain

Mature Water slows down The water is directed sideways, widening the valley Meanders or curves develop Better drainage and flood plain developed

Old Water moves very slowly Little gradient Extreme meanders and oxbow lakes Very good drainage and a wide flood plain Rivers can rejuvenate and become young again

Floods

Terms Flood – Occurs when water spills over the banks into the floodplain Floodplain- Flat area of land next to the river Natural Levee – The sediment left behind from previous floods that protect the banks Flood Crest – The highest point the flood water reaches above normal