5.1 Weathering and Erosion
Weathering and Erosion
First thing’s first! There’s a lot of new vocabulary associated with Sedimentary Rocks and the processes that create them. This is the place to make sure you are familiar with all of it. Finish the exercises below to get one step closer to becoming a Sedimentary Rocks Master!
The main ingredients of clastic and inorganic chemical sedimentary rocks come from the breakdown of other, existing rocks on Earth’s surface through a process called weathering. Erosion is the process of carrying those sediments away from their original source, either by wind, rivers, landslides, etc. As you have learned in your assigned reading, there are two main types of weathering: physical and chemical.
Physical Weathering involves the physical breakdown of rock into smaller pieces, or sediments (also known as clasts!) This is where the Clastic Rocks come from.
Chemical Weathering involves the chemical reaction of rock with water, the atmosphere, or organisms to break down the rock into new materials. Oftentimes, new minerals result, and the rock will dissolve into ions. This is where the Chemical Rocks come from.
Below are some assorted types of weathering. Your job will be to sort these according to Physical and Chemical Weathering.
Hydrolysis: The interaction of rock with water to produce dissolved ions and clays.
Oxidation: The interaction of rock with the oxygen in the atmosphere to cause rusting of some minerals.
Abrasion: The action of water or wind against the rock that causes the breakage of sediments along planes of weakness.
Dissolution: The contact of acidic water with rock that dissolves or eats away at the existing rock.
Exhumation: The sudden removal of overlying pressure from a rock that causes it to expand and crack along areas of weakness.
Ice-Wedging: The breakage of rock caused by the expansion of water in its cracks when it freezes as ice.
We will not dive too deeply into the different processes of weathering here, but we will explore the consequences of weathering different types of rocks.
First, let’s look at this familiar rock sample from last week’s lab.
The rock in the above question is mostly composed of minerals such as
Quartz (SiO2),
Plagioclase (CaAl2Si2O8), and
Orthoclase (Alkali Feldspar, KAlSi3O8).
Although we tend to think of rocks as solid and strong, different rocks can have very different responses to weathering! Let’s see how two different types of rocks respond to chemical weathering. In these videos, a dilute amount of hydrochloric acid is dropped onto two different rocks. Keep in mind that our rain on this planet is also slightly acidic!!
