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Hi there! I am Studyfin, your geography buddy. Today we will look at how mountains and rivers form, and how they reshape the land around them over time.
Earth's outer shell is broken into tectonic plates that creep a few centimeters each year. Where two plates push against each other, the crust buckles and folds upward, and over millions of years ranges such as the Himalayas and the Andes rise.
A river begins at a source where rain and melting snow collect in the highlands. Gravity pulls the water downhill through a channel to its mouth, and the whole area of land that drains into that channel is called its watershed, or drainage basin.
As it moves, a river erodes rock and soil upstream, carries that sediment along, and deposits it downstream, building floodplains and a delta where it meets the sea. Weathering and erosion wear mountains down at the same time tectonic forces push them up.
Let's practice reading a physical map. How can you tell which way a river flows, and why do mountain ranges stand where they do?
- Step 1: Read the elevation key. Brown and white shading marks high land and green marks low land. The Rocky Mountains run down western North America because plates collided and crumpled the crust along that edge.
- Step 2: Find a river's source in the high shaded area and its mouth where it reaches the sea. Because water always moves from higher elevation to lower, the river flows from source to mouth.
- Step 3: Look closely at the continent of North America. Find the row of brown triangle symbols running down the western side. These triangles show us the Rocky Mountains!
