Summary

This video explains the forces that go into build mountains, and what factors limit the height to which they can grow. Tectonic plates and the fact that they are floating on the Earth’s mantle is one of these limiting factors. Natural processes go into this limitation on mountain height also, processes involving tectonic plate movement or water streams eroding and weakening the mountain.

Why Watch This Video?

1. Have you ever wondered why the different heights of mountains exist on Earth?
2. Would you like to know learn how the top of a mountain can fall off?
3. Have you ever been confused by what happens when continental plates collide into one another?

Key Terms

Continental Crust: the part of Earth’s tectonic plate that forms the landmasses, it is generally thicker than oceanic crust.

Mantle: makes up most of Earth’s volume, envelopes the core of the earth. Is denser than the crust which allow the crust to sort of float on the top of the mantle, or the asthenosphere.

Tectonic Plates: a large chunk of rock that can be composed of continental crust and/ or oceanic crust on top of a layer of the uppermost mantle; also called lithospheric plates.

Loose Ends

Why the interior of the Earth is hotter and melts continental crust as it sinks into the Earth

The interior of the Earth is hotter because the pressure increases at greater depths. As continental crust sinks into the Earth the pressure increase raises its temperature until the rock passes its melting point.

What forces are pushing on the tectonic plates?

The main force pushing plates…is actually a pull. It’s called slab pull, and it’s the pull that comes from the edge of tectonic plates falling into the mantle. As the edge falls in, it drags the rest of the plate along. Convection is sometimes given as the mechanism behind plate motion, but convection is more important as a way of bringing heat from Earth’s core to the layer beneath tectonic plates. The heat makes the layer weak, allowing plates to move, kind of like how you can slide the cookie parts of an Oreo around on the filling layer.

Why do Earth’s continental plates float on the mantle?

The continental plates float on the mantle because the rocks that compose them are less dense than the mantle which means the continental plates will not sink.

Self-Test Questions

Scroll down for the answers.

1. What factor limits the height of the hypothetical conical mountain talked about in the video from 45km tall to 15km tall?

1. The weight of the mountain
2. The density of the mountain
3. How many streams are on the mountain
4. How wide the mountain is

2. What can happen to mountains as a result of a collision between two tectonic plates?

1. They fall over
2. They get stronger
3. Fractures and cracks can appear
4. Collisions do not occur between tectonic plates

3. What can cause cracks and fractures in rock and mountains to expand?

1. Prolonged dry spells
2. Heavy rains
3. Freeze-thaw cycles
4. Heating by the sun

4. What happens to continental crust as more weight is added above the surface?

1. It distributes evenly over the land as more weight is added
2. It only builds upward with the addition of weight
3. It forms a new tectonic plate
4. The crust will start to sink into the mantle as more weight is added

Answers

1. Answer A is correct because the video says that if the mountain were any taller than 15km it would just start sinking into the mantle and breaking off the crust.

2. Answer C is correct, fractures and rocks can appear weakening the strength of the mountain.

3. Answer C is correct, over millions of years continual freezing and thawing can expand cracks and fractures.

4. Answer D is correct, as more weight is added to continental crust it will start to sink into the mantle.