How Water Shapes the Land: Crash Course Geology #9

One of the main ways water shapes the Earth is through weathering, the process of wearing down rock over time.

And that can look like a bunch of different things.

Chemical weathering, for instance, occurs when chemical reactions caused by water or other substances, like acid that oozes from lichens, transform or destroys the minerals in rock.

This is how we get karst landscapes, areas mostly made of carbonate rock, which dissolves when touched by a weak acid.

And you know what's slightly acidic? Rain! As it falls and gets absorbed into the ground, it slowly dissolves the rock little by little, Swiss cheese style, over thousands of years.

Then we end up with incredible caves like this in Slovenia.

Water is also involved in physical weathering, a process where natural forces or living things break or wear away rock.

In the case of water, it can do that through sheer brute force or by expanding where it freezes, like it does with this limestone in the North Pennine region of England.

So weathering can make big changes to the landscape, as can its counterpart, erosion.

Weathering happens when physical, chemical, or biological processes break or transform a rock.

Erosion happens when gravity, wind, or water moves those broken off rock bits, known as sediment, somewhere else.

Often erosion is caused by runoff, water that can't be absorbed by already soaked land, so it flows across the surface.

Weathering and erosion join forces to create some amazing features, like these ones in Bryce Canyon National Park.

A cap of hard rock on the plateau protects all the softer rocks below.

So physical weathering by rain and snowmelt form steep cliffs and narrow, rocky walls.

Then, as temperatures rise during the day, water seeps into the cracks in the rock.

As temps plunge below freezing at night, the water turns to ice, wedging the rocks apart.

Eventually, the process breaks off chunks, creating windows in the steep, rocky walls.

The roof of each window collapses, leaving these strange towers behind.

And chemical weathering helps to round the rocks into a variety of bulbous shapes.

These features go by several equally fantastic names depending on their location, including hoodoos, tent rocks, and fairy chimneys.

You can also see the effects of weathering and erosion in the ways rivers change shape.

Over time, a river carves a groove in the land, whether a V-shaped valley, a steeply walled slot canyon, or some other shape.

But all that sediment cut from the terrain has to go somewhere.

The river whisks that sediment downstream, the current slowing down as it enters a larger body of water or flows into a flat plain.