Weathering and Erosion

By: Lauren and Makayla

What is weathering?

Weathering is when rocks slowly overtime breakdown or wear away, this is caused by physical force. There are 3 types of weathering, Physical/Mechanical weathering, Chemical Weathering, and Biological Weathering.

Mechanical/physical Weathering

Physical weathering is caused by physical changes in the world. Changes could be things like temperature ,freezing, thawing, wind, rain and waves. An example of temperature is when a rock is heated and cooled repeatedly, it cracks the rock. Eventually parts of the rock falls off. Another way of Mechanical/physical weathering is wind. Wind blows particles of sand against the rock. After a while the rock starts to wear away. Freeze-thaw is also a form of mechanical/physical weathering. Water gets into the rock, heats the rock, and cools the rock. The rock expands, and contracts, causing parts of the rock to break away. The last example involves rain, and waves. Rain, and waves crash against rocks with force, eventually over time causing them to break down.

Chemical Weathering

This is when chemicals break down different rocks. Chemicals on the rock react with other chemicals that the rock comes in contact with, causing it to break down. Rainwater is one of the ways rocks break down by chemical weathering. Rainwater contains a small amount of acid, so when rocks get rained on the chemicals mix, and cause a chemical reaction. This chemical reaction creates new soluble substances, and once these substances wash away, you are able to see that some of the rock has broken down. However some hard rocks such as Granite and Gabbro cannot be broken down fast by chemical weathering. It takes time, and can only slowly be broken down. This is because rocks like this don't have a lot of chemicals that will cause a chemical reaction, making them harder to be broken down by chemical weathering. For example Chemical weathering can hollow out caves, and make cliffs fall.

Biological Weathering

Biological weathering is when things such as animals or plants break down rocks. An example of a way plants can break down rocks are by their roots. Plant roots can grow into rocks, growing stronger and stronger. Eventually causing the rocks to crack, or for parts of the rocks to fall off. An example of animals causing biological weathering is burrowing animals. Burrowing animals such as rabbits, can burrow into rocks, causing the rocks to split. Over time the cracks get bigger and bigger causing part of the rock to break off. An example of Humans causing biological weathering is walking. All humans have to do to cause this is walk on the surface, overtime the rock that keeps getting walked on eventually starts to break down.

What is Erosion?

Erosion is when things get moved from one place to another by different forces such as water, wind, and ice. It can form some of the different land forms such as mountain peaks, valleys, and coastlines.

Erosion by Wind

Erosion by wind occurs by Wind carrying (for example) dust, sand, and volcanic ash from one place to another. The sand, dust, and volcanic ash slam against the rock wearing away the “soft rock”. The amount of sediment that wind can carry varies one how much wind/force you have. If you have a strong wind it can carry larger/heavier objects. But if you have little wind, you can only carry small/light things. Erosion by wind can make sand dunes, when the wind picks up particles such as sand and moves the sand around eventually creating a sand dune. It can also move houses, if you have a strong enough wind/force. Wind erosion has had quite an effect on other structures. For example, a mountain range in Australia was completely eroded away. Wind and water carry all different sizes carving and wearing away the rocks completely.

Erosion by Water

This is when things get moved from one place to another by the force of water. Erosion by water can lift the weight of objects, and move them to other places. For example moving water can either wear away some rocks because of its force, or it can pick up and carry its weight, dropping it off eventually, somewhere else. Erosion by water can turn rocks into pebbles, and pebbles into sand. The sediment size that can be carried is dependent on how much water you have, and the speed of the waters movement. If you have a lot of fast, rushing water you could (for example) lift houses. If you have a little of slow, still water then you could only carry the weight of small particles. It can form coastlines, beaches, shores, and valleys. For example waves in the ocean can crash into beaches, collecting particles of sand beneath the waves. This can create coastlines to either go farther back or closer.
Water Erosion Lab
Above is an example video of how water erosion works. This is an example of erosion by water because, the water that is being poured onto the sediment is carrying the sediment down to the bottom of the container, moving the sediment from the top to the bottom.

Erosion by Gravity

Gravity is a force that pulls things downwards. Erosion by gravity is when things get moved from one place to another by gravitational pull. Things such as rocks, and water. Erosion by gravity is very dangerous because it can cause things to move at a quick pace. Causing things such as landslides. The sediment size that can be carried varies on how much force, or gravitational pull you have. For example if you have a lot of force, you can move a big rock. But if you only have a little force, you can only move a little rock. Gravity pulls rocks down, so when rocks cant support whats above them, they get pulled down. This causes a sinkhole. Rocks on the top of mountains can eventually get pulled down because of the gravitational pull. When several rocks fall down the mountain side at once, its causes a landslide.

Erosion by Glacier

This is when things get moved from one place to another by glaciers. When glaciers move they pick up everything in their path. They can pick up things like rocks, or boulders. The rocks and sediment that have been picked up, gets dragged across the ground carving out things like valleys. The sediment gets stuck onto the glaciers because they freeze and stick onto them. The rocks dig out the ground. A glacier can carry all different sizes of sediment, depending on how big the glacier is. Some examples of erosion by glaciers are the Finger Lakes in New York, and the Fjords on the coast of Scandinavia. The fingers lakes were formed because the glaciers carved into the ground once sediment froze onto the glacier.