weathering - Weathering and Soils Page 1 of 7 EENS 1110...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
This page last updated on 30-Jan-2012 EENS 1110 Physical Geology Tulane University Prof. Stephen A. Nelson Weathering and Soils Earth is covered by a thin veneer of sediment. The veneer caps igneous and metamorphic basement. This sediment cover varies in thickness from 0 to 20 km. It is thinner (or missing) where igneous and metamorphic rocks outcrop, and is thicker in sedimentary basins. In order to make this sediment and sedimentary rock, several steps are required: z Weathering Breaks pre-existing rock into small fragments or new minerals z Transportation of the sediments to a sedimentary basin. z Deposition of the sediment z Burial and Lithification to make sedimentary rock. Each Step in the process of forming sediment and sedimentary rocks leaves clues in the sediment. These clues can be interpreted to determine the history of the sediment and thus the history of the Earth. Weathering Geologists recognize two categories of weathering processes 1. Physical Weathering - disintegration of rocks and minerals by a physical or mechanical process. 2. Chemical Weathering - chemical alteration or decomposition of rocks and minerals. Although we separate these processes, as we will see, both work together to break down rocks and minerals to smaller fragments or to minerals more stable near the Earth's surface.Both types are a response to the low pressure, low temperature, and water and oxygen rich nature of the earth s surface. Physical Weathering The mechanical breakup or disintegration of rock doesn't change mineral makeup. It creates broken fragments or detritus. which are classified by size: z Coarse-grained Boulders, Cobbles, and Pebbles. z Medium-grained Sand z Fine-grained Silt and clay (mud). Physical weathering takes place by a variety of processes. Among them are: z Development of Joints - Joints are regularly spaced fractures or cracks in rocks that show no offset across the fracture (fractures that show an offset are called faults). { Joints form as a result of expansion due to cooling or relief of pressure as overlying rocks are removed by erosion. Page 1 of 7 Weathering and Soils 1/30/2012 http://www.tulane.edu/~sanelson/eens1110/weathering.htm
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
{ Igneous plutons crack in onion like exfoliation layers. These layers break off as sheets that slide off of a pluton. Over time, this process creates domed remnants. (See figure B.4 in your text) Examples: Half-Dome (CA.) (see figure 22.12a in your text) and Stone Mountain (GA.). { Joints form free space in rock by which other agents of chemical or physical weathering can enter. z Crystal Growth - As water percolates through fractures and pore spaces it may contain ions that precipitate to form crystals. As these crystals grow they may exert an outward force that can expand or weaken rocks. z Thermal Expansion - Although daily heating and cooling of rocks do not seem to have an effect, sudden exposure to high temperature, such as in a forest or grass fire may cause expansion and eventual breakage of rock. Campfire example.
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern