Erosion is a key part of the Rock Cycle. It is responsible for forming much of the interesting landscape that is around us. Erosion is also a major problem as people live in areas in large numbers and get used to the environment being in a certain way. People can do things to increase erosion or slow it down.
Erosion happens mainly as a result of weathering – the effect of WATER, TEMPERATURE and WIND on the landscape.
ACID RAIN: chemicals in the air combine with precipitation. Water causes much erosion. When it falls as acid rain, it can dissolve rocks that are sensitive to acid. Marble & limestone weather when exposed to the rain.
LEACHING by ground water: water soaks into the soil, picks up chemicals. This allows the water to leach or dissolve rocks it comes in contact with at bedrock.
WAVE ACTION at the beach: the waves tumble rocks. The action of waves on a beach causes much erosion. The waves pound on the rocks & over time, cliffs crumble. That is why you will often find sand & little pebbles on beaches. Rocks get ground down by the sand particles already on the beach, rocks smash against each other & break.
FAST MOVING WATER: rocks get picked up & carried when water runs swiftly. Rushing water, like what you find in rivers that move quickly in the mountains or strong waves on the shores of oceans, roll rocks around. This causes the sharp edges of the rocks to get knocked off & that is why river rocks are so smooth & beach pebbles look polished. Rivers with a lot or rushing water can cause mud slides and erode river banks.
GLACIERS: large sheets of ice pick up large rocks, scrape bedrock. Rocks tumble in under-glacier rivers when glaciers melt.
PRECIPITATION / FLOODS: heavy rain can cause floods which move & break rocks. When the rain falls very heavily, as in monsoons, then flooding can happen.
The FREEZE / THAW CYCLE causes mountains to crumble over time and large rocks to break down into little rocks.
When water gets into cracks in the rocks, this water expands during the freeze cycle, making the cracks bigger. Then when the cracks fill up with water in the thaw period. This allows more water to go deeper into the rock which will make the rocks split apart when they freeze again.
The power of frozen water expanding can be seen when you leave a glass bottle filled with liquid in the freezer. <.p>
Wind, when it carries bits of sand and grit, can blast away layers of rocks. The wind can easily pick up little bits of sand and then sandblast the rocks that are in the wind's way.
Sometimes only the soft layers of the rock are eroded, leaving interesting shapes.
This kind of erosion usually only happens in very dry, desert like areas.
OTHER CASUES OF EROSION
- How hard / tough mineral is: softer, more friable rocks and minerals break up easily
- Plant roots growing: plants get nutrients from the soil, seek out certain minerals like potash, apatite for fertilizer, small roots go in cracks & break up mineral or rock when the root grows bigger
- Rock Falls: rocks tumbling down from a cliff or steep mountainside cause rocks to break up
- Contact with soil: certain soils have chemicals in them that react with the chemical make up of rocks
- Photo of what damage erosion does http://www.erosionseed.com/
Understanding Erosion & Sedimentary Rocks by Looking at Lint!
You may have a difficult time imagining something solid like rocks wearing down over time - but everything does. If you take a look in the lint trap of your dryer, you will see that your clothes are being worn away as they tumble in the dryer. In fact if there is enough lint - you will see how these bits have been laid down into layers - just like sediments at the bottom of the lake. You will see layers of different colors because the clothes you dried were different - just like you will see different layers of rocks in sedimentary rocks. What is even more interesting is that if you scrunch up the lint a bit like in the picture here, you can see the layers of lint bending - just like the layers of rock are bent. Look carefully at the rocks in road cuts and you sill see layers of rocks that have been folded just like the lint in your dryer. Neat eh?!
This is what lint looks like that comes out of a dryer.
SOIL, SAND & DIRT
When rocks break down into smaller & smaller pieces, they turn into sand. If you look at the sand under a microscope, you will see that sand is made up of the same minerals as the rocks that the sand came from.
When plants start to sprout up in sand, it is turning from being just small bits of rock to being soil. Soil is very important to life on earth. It supports plant life. We could not live without plants. Soil is made up of sand and decomposing plants and animals. Soil has many names including: clay, silt, mud, dirt, topsoil, dust, potting soil and humus.