CH14 WEATHERING AND EROSION MRS. KUMMER SPRING, 2016

WEATHERING-WHAT IS IT? 2

WEATHERING-HOW DOES IT HAPPEN? 3

MECHANICAL WEATHERING-3 MAIN TYPES 1.Ice Wedging: Water seeps into cracks or rocks and freezes 2.Organic Activity: Plants and Animals doing the breakdown of rocks: Roots growing in cracks of rocks or prairie dogs digging a burrow which exposes more rock surface for mechanical weathering to occur 3.Abrasion: Rocks colliding with each other to break down rocks using 3 main agents: Gravity: Rocks falling….check out Louisville KY expressways… Running water: Currents of streams/rivers tumbling rocks around Wind: Wind blows tiny particles (like sand) on rock faces 4

CHEMICAL WEATHERING-5 MAIN TYPES 1.Hydrolysis-changing a rock’s chemical composition when the rock reacts with water Ex: a lot of your clay soils are made by water reacting with a mineral, like feldspar Leaching is a big problem of hydrolysis…the carrying and depositing of the dissolved minerals from Hydrolysis to other lower layers of rock…mineral ore deposits like bauxite 2.Carbonation-CO 2 in air dissolves in H 2 O to make Carbonic Acid, H 2 CO 3 Ex: carbonic acid reacting with calcite to make calcium bicarbonate deposits…the insides of caves 3.Oxidation-when metallic elements combine with oxygen Ex. 4Fe + 3O 2 →2Fe 2 O 3 4.Acid Rain-when water in the atmosphere combines with air human-made waste gases such as NOx and sulfur Note: all rainwater is naturally acidic, as it contains dissolved CO 2 5.Plant Acids-some plants like lichens and mosses produce a weak acid Since lichens and mosses grow on rock surfaces, they can dissolve rocks 5

HOW FAST DOES WEATHERING OF ROCK OCCUR? Generally, rock weathering is very, very slow process (ex. Caves can take ~30 million years to form) 4 main factors impact the rate at which rock weathering occurs: 1.Rock Composition: Slowest rocks are igneous and metamorphic rocks (your hard rocks on Moh’s Scale like quartz)…fastest rocks are sedimentary rocks like Limestone 2.Amount of Exposure: typically your surface rocks weather faster than buried rocks (sun, wind, rain, etc. can’t impact buried rocks as quickly) 3.Climate: the greatest effect on the rates of weathering with hot/cold altering seasons 4.Topography – surface features of the earth determine rate of weathering…is the rock on a slope and can fall? Is it in a flat field, with no trees, exposed to wind/sun/rain? 6

THE BASICS OF SOIL What is soil? Dirt and rock combined…3 types of rock in soil: 1) clay, 2) sand, and 3) silt Where does soil originate? 1) Clay comes from Feldspar weathering 2) Sand comes from Quartz weathering 3) Silt comes from water currents depositing the gritty feeling soil to riverbanks, marshy areas How do we study soil? We look at soil profiles, cross-section of chunk of soil to observe its layers, which scientists call horizons 7

THE TYPICAL SOIL PROFILE IN MICHIGAN-5 LAYERS O Horizon The Organic Layer -The surface layer with grass,leaves,twigs, dirt,etc. -Black/Dark Brown due to all the decay, or humus A Horizon The Topsoil Layer -Still organic, but now has small rock particles -Black/Dark Brown due to all the decay, or humus -Most root activity for all plants is in this horizon E Horizon The Subsurface Layer Zone of Leaching -Water and minerals react dissolving minerals. The dissolved minerals are washed (leached) down to other layers, leaving a concentrated salt/silt layer -Bleached/No Color/White-ish or Gray B Horizon The Subsoil Layer -Dense Layer where leached minerals accumulate, no organic matter left -Light-colored/Gray C Horizon The Bedrock Layer -Contains parent material, just starting weathering process -Brown Color 8

SOIL AND CLIMATE So what does a soil profile look like in Florida (tropical)? What does it look like in Alaska (arctic)? Thick O Horizon Thick A Horizon Thin C Horizon Thin O Horizon Thin A Horizon Thick C Horizon Tropical Climate Soil Profile Arctic Climate Soil Profile NOTE: Topography also impacts soil profiles. Question: Does a slope of a hillside look more like Tropical or Arctic? 9

SOIL EROSION Erosion: the process of transporting the weathered products Four main agents to aid erosion: gravity, wind, glaciers, and water Typically, erosion is an invisible natural occurring process New residual soil forms as fast as existing soil erodes Until humans and unusual climate conditions upset this balance Then it accelerates…oh no! 10

ACCELERATED SOIL EROSION-BY HUMANS Poor Farming and Ranching Methods destroy soil exposing O and A horizons to full effects of erosion Gullying: Plowing furrows, or narrow rows over and over, allowing water to collect and rush through during rainfall Clearing Trees and small plants from farming region…convenient for a tractor or combine but terrible for the O and A horizons Allowing animals to over-graze, clearing O horizon and exposing A horizon 11

Sheet Erosion: when continuous rainfall evenly washes away the topsoil, stripping away parallel layers of A horizon, eventually leaving B horizon on surface and exposed This happens today in Arizona, California, Nevada, New Mexico and Texas during high drought seasons This happened in in Oklahoma called the Dust Bowl ACCELERATED SOIL EROSION-BY HUMANS 12

ACCELERATED SOIL EROSION-BY HUMANS AZ DUST STORM 2012OK DUSTBOWL1930S 13

SOIL CONSERVATION-GOOD FARMING METHODS Four main methods farmers can use to help maintain fertile soil: 1.Contour Plowing: plow the soil in circular bands that follow the natural contour (shape) of the land….this can prevent water from flowing directly down slopes that can start gullying. 2.Strip-cropping: plant crops in alternating rows: Ex. One row of corn, next row of cover crop like alfalfa (covers the whole surface). The cover crop row absorbs and holds the rainwater which helps prevent washing soil away. 3.Terracing: Building steplike ridges into the hillside to grow crops. This method heavily used in Asian regions to grow rice. It prevents the water from flowing directly downward. 4.Crop Rotation: Grow one crop one season and then a different one the next season. Ex. Grow corn one season then a cover crop (like alfalfa) the next. This gives time for small gullies formed when growing the corn time to fill in with soil the next season. 14

SOIL CONSERVATION-GOOD FARMING METHODS 15

GRAVITY AND EROSION 16

GRAVITY AND EROSION-PICS & VIDEOS Landslide Rockfall Mudslide Mudflow in Austria Slump Solifluction in Russia 17 Talus: small rock particles that fall from a landform and pile up at base.

EROSION AND LANDFORMS 18

EROSION AND LANDFORMS 19