'weathering' of this WestTennessee SHALE ROCK EC EarthCache
'weathering' of this WestTennessee SHALE ROCK EC
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As an Earthcache, there is no container to discover. Rather, with this cache, you discover something interesting about the geology of the area. To receive CREDIT for this 'find' please e-mail me at my profile the answers to the following questions. PLEASE send your answers shortly after you LOG your find as I do not wish to DELETE your find!
REQUIREMENTS for this Earthcache are:
1- Weathering is the direct result of ________. The greatest weathering agent is ________.
2- Estimate the height of this shale rock protrusion.
3- Determine if the 'weathering' that you see is PRIMARLY mechanical or chemical weathering.
4- List the TYPES of mechanical & chemical weathering that you observe.
5- Do you see 'NEW' soil being 'CREATED' at the base of this shale rock protrusion as a result of 'weathering'?
6- How many layers of shale sediment do you observe?
(There is room for safe off-road, pull-off parking).
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This EarthCache is located in the western Tennessee River basin and relates to the shale rock protrusion at the listed coordinates which is just a few feet off the edge of this county road.
One of our formations in Tennessee is shale, which at any point in the state is it over a hundred feet in thickness. This shale sediment was formed by water & erosion in another area and then brought here and re-deposited by large amounts of water. This specific formation of shale is an out-croping which is often found on both sides of the weatern Tennessee River.
This shale protrusion is the result of sedement layering that took place many thousands of years ago, built up successively in the order in which you now see them, when the water from the now Tennesse River was so much higher. The denudation, or the cutting and washing away, as geologist express it, in this case by water, has formed this valley.
In this earthcache that you are looking at, you are trying to determine the reasons for the 'weathering' that is taking place.
CLIMATE & WEATHERING:
Weathering is the direct result of the CLIMATE. It will determine the rate and the type of weathering that occurs to these shale rocks. The greatest weathering agent is WATER. The amount of precipation in this area will determine the amount of weathering that can occur.
The rate of weathering depends upon three main factors:
1- The minerals being weathered and there resistance to weathering
2- The climate
3- The amount of surface area exposed
Scientist can use known rock surfaces to measure weathering rates. For example, buildings, tombstones, and monuments have known dates of construction, and these rock surfaces can be examined.
Weathering is the decomposition of the earth's rocks, soils, and minerals through direct contact with the atmosphere. Weathering occurs without movement, meaning that erosion is NOT considered to be weathering, though it may have caused the environment for weathering.
There are TWO TYPES of weathering - MECHANICAL (PHYSICAL) and CHEMICAL.
MECHANICAL weathering - involves the breakdown of rocks and soils through direct contact with atmospheric conditions such as water, ice and preasure. Mechanical weathering is a major cause of the DISINTERGRATION of rocks. The rock size is broken down into smaller particles but the rock components are NOT altered.
CHEMICAL weathering - involves the direct effect of atmospheric chemicals or biologically produced chemicals in the breakdown of rocks, soils, and minerals. The composition of the rock components DOES change in chemical weathering.
The minerals left over after the rock breaksdown combined with organic matter creates soil. The mineral content of the soil is determined by its parent sources. Thus, a soil derived from a single rock type can often be deficient in one or more minerals for good fertility, while a soil weathered from a mix of rock types often makes a more fertile soil.
TYPES OF MECHANICAL WEATHERING:
THERMAL EXPANSION - This type of mechanical weathering happens when there is a great CHANGE in temperatures on a cyclic basis as we have in the western Tennnessee River basin. The stress of the temperature change causes the peeling off of the layers of the rock into sheets. Thermal expansion is of course increased by moisture.
FROST DISINTERGRATION - This happens in environments with alot of moisture & humidity like this area of western Tennessee has, and where the temperature often fluctuates above and below freezing. When the water freezes it crystalizes and expands, producing stress on the rock. Limestone and shale, like this shale protrusion, are especially vulnerable to this type of weathering.
BIOLOGICAL WEATHERING - Liviing organisms may contribute to mechanical as well as chemical weathering. The attachment of organisms to the rock surface enhances physical as well as chemical breakdown of the surface microlayers. On a large scale, seedlings sprouting in a crevice and plant roots excert physical preasure as well as providing for water and chemical infiltration. Burrowing animals and insects disturbe the soil layers adjacent to the bedrock surface increasing water and acid infiltration too.
TYPES OF CHEMICAL WEATHERIING:
DISSILUTION - Rainfall is acidic because atmospheric carbon dioxide dissolves in the rainwater producing weak carbonic acid. It is the cause of acid rain, and the acid level is 2-3 times the normal.
CARBONATION - This takes place when rain combines with carbon dioxide. It has an effect especially on limestone because the weak carbonic acid formed reacts with calcium carbonate.
BIOLOGICAL/CHEMICAL WEATHERING - A number of plants and animals may create biological/chemical weathering. The decaying remains of plants and the waste of animals form organic acids which when dissolved in water causes chemical weathering.
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