Forces that Cause Change in Landforms

1. Forces that Cause Change in Landforms

2. What is weathering? It is the slow process of breaking down rocks.

3. There are 3 types of weathering • Physical/ Mechanical • Chemical • Biological

5. Chemical weathering breaks down the bonds holding the rocks together, causing them to fall apart, forming smaller and smaller pieces. Chemical weathering is much more common in locations where there is a lot of water. Click me to see something cool!

6. Erosion is the process of carrying weathered sediments away from a place. Click me to see something cool!

7. Deposition is the dropping of the eroded sediments in a new place.

8. An easy way to remember the order of the forces that cause change to landforms… Think of the abbreviation for Wednesday: W E D EATHERING ROSION EPOSITION

9. Erosion and deposition destroy old landforms and create new ones. Moving water, wind, moving ice and gravity cause erosion and deposition.

10. Moving water… As water moves across the land, it carries away soil, sand and small rocks. When the water slows down the materials fall out and are deposited. This is how deltas and beaches are formed. Moving water is the major cause of erosion.

11. Wind… Wind can move and deposit particles of rock, soil, and sand. The amount of erosion caused by wind depends on the speed of the wind and how long it blows. Wind builds land when it deposits materials.

12. Moving ice… Glaciers move down a mountain at a very slow pace. As the glacier moves, it has to tear itself away from the rock surface, often “plucking” some of the rock with it. These materials trapped in the ice, cut away more land as the glacier drags them along. If a glacier melts and shrinks, the deposited sediment is called till and makes great farmland. When a large amount of till is accumulated, it’s known as a moraine. Any water left forms lakes, ponds and streams.

13. Gravity… Mass movement of soil occurs on steep slopes under the influence of gravity. The process involves the transfer of slope-forming materials from higher to lower grounds due to self weight.

14. Let’s review each of our 6 stations and determine what type of weathering it is or if its an example of erosion or deposition.

15. Station 1 – Blowing Around This is an example of physical/mechanical weathering by the wind. The sandpaper and salt in this center simulates the wind. Since this takes a very long time to occur, the chalk is moved through the salt to simulate the wind with dust and other particles (salt) blowing against the rock (chalk).

16. Station 2 – Shake it Up The results of this activity are another example of physical weathering but by water. Rocks in streams bang and rub against each other becoming smooth and rounded. The part of the rock that rubs and grinds off is carried away by the water (erosion).

17. Station 3 – Ice on the Move Physical weathering through glacial movement was illustrated when the ice containing sand was rubbed against the rock. The gravel and rocks frozen in glacial ice weather the rocks as the glacier passes over it. As the glacier continues moving, it moves the eroded material with it. This action, over thousands of years, causes glacier carved valleys that are U-shaped. 1941 2004

18. Station 4 – Plaster and Ice This activity simulates what happens when water is frozen in cracks within the rock. As the water freezes, it expands causing the crack in the rock to expand. As this happens time after time, the rock splits apart. This is physical weathering by ice and water. When the rock breaks apart, it erodes away through water movement and/or gravity.

19. Station 5 – Chemical and Physical • Cup A – chemical weathering; The chemical composition of the chalk changes due to it’s exposure to the acids in the vinegar. • Cup B – chemical weathering by water; The water breaks down the chalk making it somewhat claylike in texture. • Cup C – physical weathering; The chalk has been broken down into smaller pieces. It is the same chalk, only in smaller pieces. • Cup D – this was the control; The chalk is in its original form prior to exposure of the elements.

20. Station 6 – The Layered Jar This is an example of both erosion and deposition. When sediments are eroded by flowing water, they are mixed together (shaking the jar). When the water flow slows, the sediments settle to the bottom of the creek, river or lake (deposition). These sediments form layers. The soil, usually rich in organic materials, settles on top of these layers. When the water recedes (moves away), rich soil is exposed where plants can grow.