Weathering & Erosion
Causes of weathering
The actual pushing or breaking of a rock
Acid eats away at rock and actually dissolves it.
Plants sometimes give off acids
Combinations of minerals have acidic effects
Humans spilling chemicals (like soda)
Dead animals sometimes give off acids
The moving of weathered sediment from place to place
Agents of Erosion
GRAVITY- The most common agent-
Things fall down….. landslides, mudslides or just plain movement downhill are all caused by gravity, a pull downward.
As wind and water and even acid weather rocks on mountains, it loosens the fragments, gravity pulls them downward so they fall down the mountain. This is why mountains are wider on the bottom and narrow on top.
Igneous Rock- first type of rock formed- born intrusive or extrusive (if in lava then it’s extrusive---- if it was in magma then it’s intrusive)
Over time the rock breaks and small pieces fall off and end up getting washed into an area where they are buried. The breaking off is called weathering and the washing away is called eroding. The pieces are called sediment.
After a long period of time the sediment gets buried and due to pressure it begins to form together….The new rock is called Sedimentary.
Sedimentary Rocks sometimes end up on the Earth’s surface and sometimes get buried deep with in the earth. Not quite in the Magma, but close enough for the heat to soften them. Now that they are soft, the pressure from above them pushes down and reforms them into a Metamorphic Rock (A rock that changed) This process takes many years!
Now, if the Metamorphic Rock ends up in the magma, it will become an Igneous Rock again, or if pieces break off of it, it might become sedimentary.
A rock does not have to go through the entire process. A sedimentary rock may end up in lava or magma and be re-cooked and become Igneous, with out ever being a Metamorphic or an Igneous can end up in magma or lava and reform into a new Igneous.
One way or another, the Rock Cycle says that all rocks can turn into each other!
There are 3 major types of rocks…
Intrusive- created inside the earth (in magma)
Extrusive- Created outside the earth (in lava)
Clastic- Fragments of other rocks form together
Chemical- Form from minerals combining with chemicals or evaporates
Foliated- bands of chemicals form
Non-foliated- no real pattern of minerals
Igneous Rocks are first to form. Igneous means from fire because these rocks form in magma.
Sedimentary are the rocks that form over time from pressure when pieces of other rocks break off.
Metamorphic rocks are rocks that get buried and form from heat and pressure but do not Melt- they just reform into new and different rocks.
Determining the type of rock is dependant on several different things….
1 - If you can see clear mineral deposits, it is probably igneous
Large- probably intrusive and small- probably extrusive
2- If it appears to have pieces of rock combining to form it is probably sedimentary
3- If it appears to have layers, it is probably metamorphic
The earth's surface is constantly being eroded. This means that rocks are broken up into smaller pieces by weathering agents such as wind, water, and ice. These small pieces of rock turn into pebbles, gravel, sand, and clay. They tumble down rivers and streams. These pieces settle in a new place and begin to pile up and the sediments form flat layers. Over a long period of time, the pieces become pressed together and form solid rock called sedimentary rock. Most sedimentary rocks form under water.
Sediments can harden into sedimentary rock in two ways.
cementing-Some sediments are glued together by minerals dissolved in water.
Igneous rock (from a latin word meaning fire) Igneous rock is formed in the mantle by magma or on the crust by lava (molten rock) being cooled and becoming solid. They may form with or without crystals either below the surface as Intrusive rocks or on the surface as extrusive or volcanic rocks. Intrusive rocks are formed inside the Earth. These rocks cook in the magma longer and cool much slower, as a result the crystals are bigger. Extrusive rocks form on the Earth's surface. They EXit the Earth, usually through a volcano. These rocks have smaller crystal grains because they cool faster. They don't cook as long. Sometimes these rocks cool so fast that they do not form crystals at all. Igneous rocks like Obsidian have a glassy look or Pumice have a rough texture and holes where crystals would have formed but gas took the place of the crystal.