What is Weathering? Weathering is the process that produces change in the surface of rocks exposed to the atmosphere and/or hydrosphere. The end result of weathering produces sediment. I took the picture at Niagara Falls (Canada)

Physical / Mechanical Weathering Breaking rock by force into smaller pieces There is NO change in the rock’s composition Total exposed surface area increases Bottom – I took at Grand Canyon (Colorado River)

Frost Action / Ice Wedging Breakup of rock caused by the freezing and thawing (expansion and contraction) of water – Ex. Pot holes Water seeps into small cracks in rocks. When the water freezes it expands creating great pressure. The crack widens and allows water to seep deeper into the rock. I took the one on the right - Yellowstone

Exfoliation Peeling away of large sheets of loosened materials at the surface of a rock Rocks formed deep in the Earth are made under high pressure – when pressure is released, rocks expand and crack Thermal expansion – repeated heating and cooling causes stress Common in granite, shale, slate, and mica Left – I took in Colorado (Dinosaur Ridge)

Plant Action Tiny roots seek out small cracks in rock Once the root hairs find a place they grow and expand Expansion causes great pressure and cracks the rock Top – I took on lava field of Big Island, Hawaii; Bottom – I took at Shenandoah National Park (Virginia)

Abrasion Wearing down rocks as they rub or bounce against each other Most common in windy areas, under glaciers, or in stream channels “Sand blasting" – wind abrasion shapes exposed bedrock (up to about 1-2 meters above the surface because sand grains are lifted a short distance) Top – I took at Garden of the Gods (Colorado)

Name that physical weathering mechanism! Wind Abrasion! Plant Action! I took bottom left - Yellowstone Water Abrasion! Ice Wedging!

SHALE SHALE SHALE WATER DOLOSTONE WHICH ROCK IS THE MOST RESISTANT TO WEATHERING? SHALE LIMESTONE SANDSTONE SHALE SANDSTONE SHALE

SHALE SHALE SHALE DOLOSTONE WHICH ROCK IS THE LEAST RESISTANT TO WEATHERING? SHALE LIMESTONE SANDSTONE SHALE SANDSTONE SHALE

Chemical Weathering Unlike physical weathering because rock composition is changed after reacting with a chemical Like physical weathering because it breaks down rock

Oxidation Oxygen in water or the atmosphere combines with iron-bearing minerals = rust Rocks become red, orange, or brown in color

Hydrolysis Water is the universal solvent – minerals commonly break apart in water Common in silicate based rocks = increase porosity and decrease stability Silicate minerals weather by hydrolysis to form CLAY Feldspar alters to clay (kaolinite) plus dissolved materials (ions)

Acid Rain Rain is naturally slightly acidic, but dissolved materials can increase acidity Sulfur Dioxide in the atmosphere dissolves in rain water forming a strong acid = sulfuric acid Corrosive forces result in loss of polished finish on buildings/structures and impacts wildlife

Carbonation CO2 dissolves in rain water as it falls through the atmosphere Forms a weak carbonic acid – reacts with minerals in rock Commonly reacts with halite, calcite, limestone, and marble Cave formation Carbonic Acid? I took this in Indian Echo Caverns (PA) Alternate video: http://news.discovery.com/videos/earth-caves-offer-climate-clues.html

Karst Topography Layers of soluble bedrock dissolves in carbonic acid Characterized by sinkholes and caves A three-story building in northern Guatemala City fell into a sinkhole in May 2010. It measured 66 feet across and 100 feet deep.