Lecture 14 - A World of Changing Environments Flashcards
Define Weathering
-The breakdown or dissolving or rocks and minerals on the surface of Earth; water, ice, acids, salts, plants, animals and temperature changes are all agents of weathering
Define Force when referring to Weathering
-Characteristics of the environment which act to encourage breakdown of rocks and minerals (e.g. water, organisms, temperature fluctuations, inherent stress)
Define Resistance when referring to Weathering
-Characteristics of rocks and minerals which condition their response to forces (e.g. chemical and physical make-up)
Describe how Freeze-Thaw Activity works
-Water seeps in to cracks in rock and freezes, thus expanding and gradually opening up the rock
-Freezing places up to 15-21kg/cm2 of stress on rock which for most far-exceeds the threshold of rocks
Describe how Insolation and Exfoliation work
-Insolation caused by thermal stress (repeated heating and cooling)
-Sharp changes in heating and cooling causes expansion near the surface of rocks
-Exfoliation caused by pressure release from thermal changes
-Typical in rocks formed at depth and in areas of high temperature and pressure change
Describe how Salt Weathering works
-Precipitation of salts in voids and their expansion
-Hydration of salt crystals and thermal expansion leads to swelling
-This gradually opens up the rock increasing the surface area
How does Dissolution work?
-Occurs when rocks and/or minerals are dissolved by water
-Dissolved material is transported away leaving behind space in the rock
-E.g. formation of caves in limestone
How does Water affect limestone?
-H+ ions dissolve CaCO3 contained in the limestone
-Both Ca2+ and HCO3- are dissolved and removed leaving a void space
-This is reversible as limestone can precipitate, e.g. as a stalacmite
What is the Difference between Bioerosive and Bioprotective?
-Erosive meaning actions which enhance weathering
-Protective meaning actions which reduce other types of weathering
