The critical agents of mechanical weathering are: Weathering cannot even begin until these rocks are uplifted through various processes of mountain building - most of which are related to plate tectonics - and the overlying material has been eroded, and the rock is exposed as an outcrop. Most metamorphic rocks are formed at depths of kilometers to tens of kilometers. Sediments are turned into sedimentary rocks only when other sediments bury them to depths more than several hundreds of meters. Intrusive igneous rocks form at depths of several hundreds of meters to several tens of kilometers. Together, these processes create two significant products, one being the sedimentary clasts and ions in solution that can eventually become sedimentary rock, and the other being the soil that is necessary for our existence on Earth. Mechanical weathering provides fresh surfaces for attack by chemical processes, and chemical weathering weakens the rock so that it is more susceptible to mechanical weathering. One is the mechanical breakdown of rock into smaller fragments, and the other is the chemical change of the minerals within the rock to forms that are stable in the surface environment. Weathering includes two main processes that are entirely different. Hoodoos at Bryce Canyon National Park, Utah. Temperatures vary widely, there is much less pressure, oxygen and other gases are plentiful, and in most climates, water is abundant.

Once a rock is exposed at the surface, which is what happens when the overlying rock is eroded, conditions change dramatically. There they experience relatively constant temperature, high pressure, no contact with the atmosphere, and little or no moving water. Except for volcanic rocks and some sedimentary rocks, most rocks are formed at some depth within the crust. Weathering is what takes place when a body of rock is exposed to the “weather” - in other words, to the forces and conditions that exist at Earth’s surface. 4 Chapter 4 Weathering and Erosion for print only Weathering

Ice wedging water falls diagram