Earth Changes: Erosion & Volcanoes

Earth's surface is always changing. Some changes happen so slowly that we never see them with our own eyes — a river takes thousands of years to carve a canyon. Other changes happen in minutes or seconds — a volcano can erupt overnight, and an earthquake can shake the ground in less than a minute. Both kinds of change shape the land we live on.

Slow Changes

Slow changes happen over hundreds, thousands, or even millions of years. Weathering is the breaking down of rock by wind, water, ice, and temperature. Erosion is the moving of broken-down rock and soil from one place to another — usually by rivers, glaciers, wind, or waves. Deposition is when those bits of rock and soil drop in a new spot, building up beaches, deltas, or sand dunes. Together these processes shape valleys, canyons, mountains, and coastlines.

• Weathering — rock cracks and crumbles from freeze-thaw, rain, and roots.
• Erosion — rivers, glaciers, wind, and waves carry pieces away.
• Deposition — carried material drops, building beaches and deltas.
• Mountain building — plates push up over millions of years.
• Soil formation — broken rock plus rotted plants make new soil.

Fast Changes

Fast changes can reshape the land in moments. A volcanic eruption sends melted rock (lava) and ash to the surface, building new land or destroying what is there. An earthquake happens when tectonic plates suddenly slip, shaking the ground and cracking roads and rock. A landslide is when a hillside breaks loose after heavy rain. A tsunami is a giant ocean wave caused by an undersea earthquake. A flash flood can carve gullies in a single afternoon.

• Volcanic eruption — magma rises, lava flows, ash falls.
• Earthquake — plates slip, ground shakes, cracks form.
• Landslide — a hillside collapses, often after heavy rain.
• Tsunami — undersea quakes push huge waves to shore.
• Flash flood — sudden water carves new gullies fast.

Inside a Volcano

Deep below the surface, melted rock called magma collects in a magma chamber. When pressure builds up, magma is pushed up through a vent. Once it reaches the air, the magma is called lava. Cooled lava hardens into new rock — over many eruptions, that rock can build a whole island. Ash, gas, and steam blast into the sky in an ash cloud that can be seen for miles.

• Magma chamber — melted rock pool deep underground.
• Vent — the channel that carries magma upward.
• Crater — bowl at the top of the volcano.
• Lava — magma once it reaches the surface.
• Ash cloud — gas, dust, and tiny rock blasted into the air.