Volcanic Landforms

Mount St. Helens is a volcano. The top of the mountain blew up in 1980. This is called an eruption. Part of the mountain fell away. A huge rock slide killed animals and trees. Thick, gray smoke filled the air. The eruption stopped. Today, the volcano is quiet and waiting. See photos below.

Mt. St. Helens, North Face & Volcano Crater
Mt. St. Helens, South Face

Volcanoes. Hot, soft rock is called lava. It comes from inside the volcano. It can be bright red and feels like fire. When it cools, it turns black. Volcanoes also have pieces of rock inside. Rock might be mixed with lava.

The top of a volcano has a round dent. Small ones are called craters. Large ones are called calderas.

Kilauea Caldera (photo left) is a huge volcano in Hawaii. Hot steam blows out of cracks in the craters.

Kilauea Volcano is the most active volcano in the world. Lava still flows.

Kilauea Caldera, Hawaii

Volcano Profiles. There are different kinds of volcanoes. Shield volcanoes are flat on top. They have lava.

Composite volcanoes have lava and broken rock. They are steep near the top. They sometimes have huge eruptions.

Cinder Cones are made of tiny pieces of rock and ash. Ash is like dust.
Ancient Cinder Cone, NE Arizona

Spatter cones are steep and bumpy. They are made of slashes of lava. They are small.

Some lava moves slow. It piles up into a plug dome.

Craters of the Moon, Idaho
Lava flows, Hawaii

Composition of Lava. Deep under the ground is very hot rock, called magma. Magma is very soft. During an eruption, magma is pushed up. When it comes outside the volcano, it is lava.

Lava flows (above photos) show where the lava ran and cooled. It can cover houses and roads.

The rock is called igneous rock. Rhyolite, andesite, and basalt are igneous.

Obsidian (photo left) is a kind of glass. It happens when lava cools fast. It is shiny and black. Obsidian is very sharp when chipped. Indians used it to make arrowheads and cutting tools.
Obsidian, Oregon
Types of Lava and Lava Flows. Thick, slow lava cools and breaks. The bumpy rocks are called aa (below left photo). Thin, fast lava, cools fast. It looks like ropes (below right photo). This lava is called Pahoehoe. Aa and pahoehoe are Hawaiian words. Can you see the lava in the pictures above?
AA lava
Pahoehoe lava
Big lava flows are called lava fields. A stream of lava can make a lava tube or lava cave (Photo, below left).
Lava Tube, Ape Cave, WA
Tree Mold, Craters of the Moon, Idaho
Pressure Ridges, Hawaii

Lava covers plants. Sometimes you can see the plant's shape in the lava. Look for the bark of the tree above. It is called a tree mold.

Pressure ridges (Above right photo) happen when lava is pressed and breaks.

Evolution of Volcanic Terrains. Wind and water wear down the rock. The sun also breaks up the rock.

Some lava is millions of years old.

Plants and animals live in old lava.

Valley of Fires National Recreation Area, New Mexico

More Information

Note: All photographs taken with a digital camera in Hawaii, Idaho, New Mexico, Oregon, and Washington.
Developed by Annette Lamb and Larry Johnson, 05/02.