Weathering & Erosion

Instructions As you watch this slide show, answer the questions you have been given.As you watch this slide show, answer the questions you have been given. Clicking the icon will take you to a movie that helps explain the concepts you are studying.Clicking the icon will take you to a movie that helps explain the concepts you are studying. Clicking the icon will take you to a website for more information.Clicking the icon will take you to a website for more information.

Instructions This slide show will take you to sites on the internet. After you have finished using the website and are ready to return to this slide show, click the button on the browser.This slide show will take you to sites on the internet. After you have finished using the website and are ready to return to this slide show, click the button on the browser. If you are viewing this from our website, just “X-out” of the website to return to the slide show.If you are viewing this from our website, just “X-out” of the website to return to the slide show.

Instructions If you see this message:If you see this message: Choose NO

Instructions If you see this message:If you see this message: Choose OK

What is weathering? Weathering is a set of physical, chemical and biological processes that change the physical and chemical properties of rocks and soil at or near the earth's surface.

More about weathering Definition – the breakdown of rock to form sediment [very small pieces of rock]Definition – the breakdown of rock to form sediment [very small pieces of rock] –Weathering happens to rocks that are NOT MOVING –Weathering is part of the Rock Cycle

There are three types of weathering Mechanical [sometimes called physical]Mechanical [sometimes called physical] ChemicalChemical BiologicalBiological

Mechanical weathering breaks rocks down into smaller pieces, but does not change the composition of the rock. Types of mechanical weathering include frost wedging, exfoliation, thermal expansion and abrasion.

Chemical weathering breaks rocks down chemically adding or removing chemical elements, and changes them into other materials. Chemical weathering consists of chemical reactions, most of which involve water.

Biological weathering is the breakdown of rock caused by the action of living organisms, including plants, burrowing animals, and lichens. A lichen is a combination of fungus and algae, living together in a symbiotic relationship. Lichens can live on bare rock, and they break down rocks by secreting acids and other chemicals.

Let’s investigate mechanical weathering first. Click to see a video clip about mechanical weathering

In mechanical weathering, a rock is broken down into smaller pieces without changing its mineral composition.

Enchanted rock is a huge example of exfoliation mechanical weathering close to home.

Observe photographs of some of the different types of mechanical weathering.

Review mechanical weathering: breaks rocks down into smaller pieces. Types of mechanical weathering includebreaks rocks down into smaller pieces. Types of mechanical weathering include frost wedging – ice in cracks expandsfrost wedging – ice in cracks expands exfoliation - rock breaks off into sheetsexfoliation - rock breaks off into sheets thermal expansion - heatthermal expansion - heat abrasion - wind, waves, rain, glaciers, and so on rub (abrade) rocks' surfaces, wearing them downabrasion - wind, waves, rain, glaciers, and so on rub (abrade) rocks' surfaces, wearing them down

Now, let’s look at chemical weathering. ayer_embedded&v=6VnVRHIV6j4http:// ayer_embedded&v=6VnVRHIV6j4

In chemical weathering, a rock is broken down by chemical reactions that change its mineral composition and physical and chemical properties. Water is most often a part of chemical weathering.

Chemical weathering happens when the minerals that make up a rock are changed, leading to the disintegration of the rock.

Physical and chemical weathering occur together. Physical weathering breaks rocks into pieces so more surface is exposed to chemical weathering which breaks it down further.

Chemical weathering happens quickly in warm, moist environments because water is needed for the chemical reactions. The warm weather speeds up the reactions.

Not all minerals are prone to chemical weathering. For example, feldspar and quartz, are common minerals in the rock granite, have very different levels of resistance to chemical weathering. Quartz doesn’t weather very easily, but feldspar does. Over a long time, it chemically changes into clay minerals.

Watch a movie about chemical weathering:

Review chemical weathering: scroll down the page to get to the topic

Biological weathering involves processes that can be either chemical or physical in nature. Biological weathering can be considered special types of mechanical or chemical weathering.

Biological weathering – What is it?

Some biological weathering processes are: 1. Rocks can break because of animal burrowing.1. Rocks can break because of animal burrowing. 2. Tree roots grow into cracks and widen them, which helps physical weathering.2. Tree roots grow into cracks and widen them, which helps physical weathering. 3. Bacteria, lichens and other organisms secrete acidic solutions, which helps chemical weathering.3. Bacteria, lichens and other organisms secrete acidic solutions, which helps chemical weathering.

Lichens on rocks cause biological weathering.

Plants growing in rocks break the rocks apart. Image Courtesy United States Geological Survey; Image source: Earth Science World Image Bank Photo ID: h7fbtb | Photographer: Bruce Molnia US Geological Survey Copyright © Bruce Molnia, Terra Photographics

How are erosion & weathering different? Weathering involves two processes [mechanical, chemical] that often work together to break down rocks. Both processes occur in place. Both processes occur in place. No movement is involved in weathering. No movement is involved in weathering.

As soon as a rock particle moves, we call it erosion or mass wasting. As soon as a rock particle moves, we call it erosion or mass wasting. If a particle is loosened, chemically or mechanically, but stays If a particle is loosened, chemically or mechanically, but stays put, we call it weathering. Once the particle starts moving, we call it erosion.

What are the different types of erosion? Wind Water Glaciers (Ice) Gravity

Water in all its forms is erosional. Raindrops create splash erosion that moves tiny particles of soil. Water moving on the surface of the soil collects as it moves towards tiny streams and creates sheet erosion.

Mass Wasting is a form of Erosion

Observe river erosion causing waterfalls

Waves in oceans and other large bodies of water cause coastal erosion. The power of ocean waves is awesome; large storm waves can produce 2000 pounds of pressure per square foot. The pure energy of waves along with the chemical content of the water is what erodes the rock of the coastline.

Wave action in Calvert County Maryland

Watch wave erosion

Erosion by wind is known as aeolian erosion (named after Aeolus, the Greek god of winds) and usually occurs in deserts. Wind erosion of sand in the desert is partially responsible for the formation of sand dunes.

Painted Desert National Monument

The erosive power of moving ice (glaciers) is actually a greater than the power of water. However since water is much more common, it is responsible for a greater amount of erosion on the earth's surface.

Glaciers

Glaciers cause erosion two ways - they pluck and abrade. Plucking takes place by water entering cracks under the glacier, freezing, and breaking off pieces of rock that are then moved by the glacier. Abrasion cuts into the rock under the glacier, scooping rock up like a bulldozer and smoothing and polishing the rock surface.

Athabasca Glacier - Jasper, Canada

Observe landscapes formed by erosion

Unless otherwise noted, the source for all photographs in this presentation is

oba.ca/~benbow/erosi on1.htmlhttp://home.cc.umanit oba.ca/~benbow/erosi on1.htmlhttp://home.cc.umanit oba.ca/~benbow/erosi on1.htmlhttp://home.cc.umanit oba.ca/~benbow/erosi on1.html