Transcript Chapter 11
Weathering & Erosion Weathering Weathering- a mechanical or chemical process that causes rocks to change by breaking them down into smaller pieces. Rocks are changed by freezing & thawing, oxygen, plants & animals 2 types- mechanical and chemical Mechanical Weathering Mechanical Weathering- the process that breaks rocks into smaller pieces without changing them chemically. Causes- ice wedging and living organisms Ice Wedging 1. Water seeps into cracks 2. Water freezes and expands, opening cracks 3. ice melts and the process repeats How do plants and animals causes weathering? Plant roots grow deep into the ground and into cracks in rock where water collects This puts pressure inside the rock and slowly wedges the rock apart Animals cause weathering too! As they dig and burrow, the animals break rock apart Examples- gophers, prairie dogs Chemical Weathering Chemical Weathering- process in which chemical makeup of rock is changed Hot and dry- slow Hot and wet- fast Cold and dry- slow Cold and wet- slow Chemical Weathering Causes- Natural acids and oxygen Natural Acids- water mixed with carbon dioxide creates carbonic acid that dissolves some rocks (limestone, dolomite, marble) Plant Acids- Plants produce tannin. When mixed with water, creates tannic acid that dissolves some minerals in rock, which can break the rock into smaller pieces Oxygen- oxygen reacts with iron in minerals (oxidation) causing them to rust and weaken. This can cause the rock to break apart Soil Soil- a mixture of weathered rock, organic matter, water and air that supports the growth of plant life Organic matter- rotted leaves, twigs, roots Things that affect the way soil forms Parent rock Topography Time Climate Organisms Parent Rock Parent rock- the original rock Affects soil formation when it is weathered Ex- limestone chemically weathered= clay soil Ex- sandstone weathered= sandy soil Topography Topography- surface features of land Steep hillsides- soil has little chance of forming Flat land- forms think soil Time It takes time for rocks to weather Can take thousands of years to form Young soils- parent rock determines the characteristic of the soil As weathering continues, soil becomes less like the parent rock Deep , rich soil- found where weathering has gone on for a long time Climate Tropical areas- climate is warm and moist- deep soils form quickly Affects organic material Deserts- soil contains little organic material Plants/animals die and decay- humus is formed Humus- dark material that helps soil hold water and provide nutrients or plants Organisms Lichens- consist of alga and fungus, are colorful patches on trees or rocks They take nutrients from the rock that break it down and form soil Other plants can grow on top of this (trees, grasses) Dead plant material builds up and adds organic matter to the soil Soil under grassy areas is often richer than soil in forests Midwest US used to be grasslands which is why it’s the best farmland