Terrace (geology)

A terrace is a landform that looks like a giant step. It has a flat part called a tread. It also has a steep side called a riser or a scarp.

These steps can be bounded on all sides by a steep slope. If the terrace is very narrow, people often call it a bench. Geologists study these shapes to understand how the Earth changes. They help us see how water and ice once moved across the land.

Many different things can create these steps. Fluvial terraces are made by rivers. A river might cut deep into the ground or move to a new path. This leaves the old flat land behind as a step. This can happen because of changes in climate or sea levels. It can also happen if the land itself moves upward.

Other steps form from different sources like glaciers or oceans.

Marine terraces show us where old shorelines used to be. First, strong waves carve a flat area into the bedrock. This flat area is called a wave cut platform. To become a terrace, this platform must move away from the waves. This happens if the sea level drops or the land rises.

Sometimes coral reefs also build up these flat areas in warm waters.

Lakes also create their own steps called lacustrine terraces. These show where an old lake shore once sat. Because lakes are smaller than oceans, these steps are usually much narrower. Some lake terraces are even the old bottoms of very deep lakes.

Glaciers can also leave steps on valley sides. These are called kame terraces and are made by melting ice streams.

There are even more special kinds of terraces to find. A structural terrace forms when soft rock wears away faster than hard rock. This leaves a flat layer of hard rock exposed like a step. Travertine terraces form from hot, mineral-rich water. These create beautiful waterfalls of stone.

You might even see tiny steps on a hill called terracettes. These small steps can be made by animals walking on the grass.