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Thursday, August 03, 2006
Freeze-thaw action occurs mainly in environments where there is a lot of moisture, and temperatures frequently fluctuate above and below freezing point—that is, mainly alpine and periglacial areas. When water that has entered the joints freezes, the ice formed strains the walls of the joints and causes the joints to deepen and widen. This is because the volume of water expands by 9% when it freezes. When the ice thaws, water can flow further into the rock. When the temperature drops below freezing point and the water freezes again, the ice enlarges the joints further. Repeated freeze-thaw action weakens the rocks which, over time, break up along the joints into angular pieces. The angular rock fragments gather at the foot of the slope to form a talus slope (or scree slope). The splitting of rocks along the joints into blocks is called block disintegration. The blocks of rocks that are detached are of various shapes depending on their rock structure. In pressure release, overlying materials (not necessarily rocks) are removed (by erosion, or other processes), which causes underlying rocks to expand and fracture parallel to the surface. Often the overlying material is heavy, and the underlying rocks experience high pressure under them, for example, a moving glacier. Pressure release may also cause exfoliation to occur. Intrusive igneous rocks (e.g. granite) are formed deep beneath the earth's surface. They are under tremendous pressure because of the overlying rock material. When erosion removes the overlying rock material, these intrusive rocks are exposed and the pressure on them is released. The outer parts of the rocks then tend to expand. The expansion sets up stresses which cause fractures parallel to the rock surface to form. Over time, sheets of rock break away from the exposed rocks along the fractures. Pressure release is also known as "exfoliation" or "sheeting". Salt crystallisation causes disintegration of rocks when saline (see salinity) solutions seep into cracks and joints in the rocks and evaporate, leaving salt crystals behind. These salt crystals expand as they are heated up, exerting pressure on the confining rock. Salt crystallisation may also take place when solutions decompose rocks (for example, limestone and chalk) to form salt solutions of sodium sulfate or sodium carbonate, of which the moisture evaporates to form their respective salt crystals.
OMG WIKIPEDIA ROCKS SOCKS. it's like, it has EVERYTHING! from celebrity names to msn shortforms! you can find ZOMG, LOL, EMO on wikipedia. and they have stuff on WEATHERING TOO.
omgah. *faints*
anyway, reason why the entry is because i love to re-read my entries OVER AND OVER AGAIN (see, eg of compulsive behaviour) and i like to blog. so might as well blog down my notes right? so that i can ahem, share it with people, and i can RE READ IT. and i can learn something too! what a genius. =D i love wikipedia! =D
and my cookies! only 1/4 is left. mum says they're too soft for her liking. she likes rock-hard ones. which i absolutely hate because i like mrs fields cookies. and if you haven't tasted them, shame on you. they're REALLY soft and nice and CHEWY. if i can bake cookies LIKE THAT. i will immediately set up my own retail cookie outlet. and i will expect to see customers STREAMING in to eat MY HOMEMADE CHEWY COOKIES! and my surname will come in handy then! =D hahahaha. im so freaking lame!
*i think i ought to spread my lameshit onto my other blog. haha! if not my post ALWAYS looks so darn boring. like me! but wth?*
nvm. oh right. weathering.
i've been stuck on geog for MONTHS. and i can say that i covered three topics. which isn't a big lie. i mean i've read up on.. whats that? population, weathering and weather and climate. which is really true. but the prob is. i can't remember?
nvm!
WEATHERING is the wearing of rocks or disintegration of rocks in situ. (without movement).
EROSION is the breaking down of rocks by natural means.
wikipedia says:
Weathering is the process of disintegration of rocks, soils and their minerals through direct, or indirect contact with the atmosphere. Weathering occurs 'in situ', or 'without movement', and thus should not to be confused with erosion, which involves the movement and disintegration of rocks and minerals by processes such as water, wind, ice or gravity.
physical weathering is the disintegration of rocks in situ.
wikipedia says:
Mechanical weathering is a cause of the disintegration of rocks or wood. Most of the times it produces smaller angular fragments (like scree), as compared to chemical weathering. However, chemical and physical weathering often go hand in hand. For example, cracks exploited by mechanical weathering will increase the surface area exposed to chemical action. Furthermore, the chemical action at minerals in cracks can aid the disintegration process.
EXFLOLIATION (or thermal expansion which i can't find in my textbook but it's found everywhere else even in marian chong's)
is caused by the constant heating and cooling of rocks. when rocks are heated up, they expand and contracts when cooled. this causes the rocks to exfloliate. think: onion.
wikipedia says:
Thermal Expansion, also known as onion-skin weathering, often occurs in hot areas, like deserts, where there is a large diurnal temperature range. The temperatures soar high in the day, while dipping to a few degrees at night. As the rock heats up and expands by day, and cools and contracts by night, stress is often exerted on the outer layers. The stress causes the peeling off of the outer layers of rocks in thin sheets. Though this is caused mainly by temperature changes, thermal expansion cannot take place without the presence of moisture.
FREEZE-THAW ACTION ( my favourite!)
during the day, water seeps into the joints or cracks of rocks, when the temperature drops at night. the water freezes and the volume is increased by 9% (or rather 8.9% but it's around there. haha) this stresses the rocks and cause the joints or cracks to expand further. during the day, the water melts and more water seeps into the enlarged cracks/joints. this process is repeated several times and the rocks will weaken and disintegrate to form scree.
wiki says:
in pressure release, overlying materials (ie soil) will be removed. due to the increasing blahbloiegw?
gosh hate this unloading shit. i don't understand at all!!! omg. wikipedia i realise, is a free-to-edit encyclopedia. so means the info may not be right at all! hmp nvm.
wiki says:
in places like the desert where water from the ground contains dissolved salts, or coastal places where sea sprays are trapped in the cavaities of the rocks. the water evaporates, leaving the salt behind as crystals in the pore spaces, cavaities and joints of the rocks. the salt crystals will grow as more seasprays are trapped or ground water is drawn up and more evaporation occurs. the salt minerals swell if they absorb water from rain and dew. build up more crystals and their swelling results stress in the rocks. this weakens their structure and they slowly break down.
wiki says:
this is so depressing!!! I CANT STUDY OMG WTF.
nevermind. i feel as if i've got tons of eyeshit. gah. and oh oh oh! NEXT WEEK i've got twodays worth of holiday! omg. =D
=D
i saw your face, in a crowded place, and i don't know what to do. cause i'll never be with you...
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