Mount St. Helens stands on eroded remains of an earlier volcano active between 2,500 and 40,000 years ago. The upper part of the cone was built around 400 years ago. Mount St. Helens is composed of lava flows and fragmented material consisting of debris. A cross-section would show alternating layers of lava, ash, and rock debris. Lava Caves form when a crust develops on the surface of fresh streams of lava. When the lava flow stops the molten drains away leaving hollow caves. Many faces including the Ape Cave were formed this way. Mount St. Helens was active until 1857. Eyewitness accounts have recorded that the volcano was very active in the 1830's and 1840's. We do not know if this can be linked with the 1980 eruption.

Information from http://vulcan.wr.usgs.gov/Volcanoes/MSH/description_msh.html

Plains:

A land form that is a large relatively flat area.

Characteristics of Plains:

-Endless flat fields of grass.

-Many are used for farming.

-Cows also graze on plains.

-The Plains found near oceans are Coastal Plains.

-The Plains found everywhere else are known as Interior Plains.

-Plains makeup one-half of the U.S.

Coastal Plains:

Broad areas along the ocean's shore.

Characteristics of Coastal Plains:

-Costal Plains are often called lowlands.

-Atlantic Coastal Plains go up the East coast and contain low rolling hills, swamps, and marsh.

Interior Plains:

-Extend from the Appalachian Mountains, to the Rocky Mountains, then to the Appalachian Mountains

-Contain rolling hills and the Central Lowlands.

-Large portions of the Interior Plains are known as the Great Plains.

-They're flat, grassy, dry, and have few trees.

-The Interior Plains are also referred to as High Plains.

Plateaus:

Landforms created next to mountains, when forces with in Earth raised high, relatively flat areas of nearly horizontal rocks.

Characteristics of Plateaus:

-Plateaus rise steeply from the land around them.

The Colorado Plateau:

-The Colorado Plateau lies west of the Rocky Mountains.

-It has only a few permanent rivers due to the plateaus dryness.

-The Colorado Plateau has a desert landscape.

-The Colorado River cut into the plateau and created the Grand Canyon.

Fault Block Mountains:

Jagged Mountains formed from huge tilted blocks of rock that are separated from surrounding rock by faults.

The Grand Tetons:

-When the Grand Tetons formed one block was tilted and pushed up. The other block pushed down.

-Landscape includes sharp jagged peaks.

Volcanic Mountains:

Created when magma with in Earth Escapes to the surface, building cones of lava and ash.

Mauna Loa in Hawaii:

-The Hawaiian Islands are peaks of huge volcanoes that stick out of the Pacific Ocean.

Up warped Mountains:

Mountains formed when Earth's crust is pushed up and eroded forming sharp peaks and ridges.

The Rocky Mountains:

-The Rocky Mountains sedimentary rock on top of crust eroded leaving behind igneous and metamorphic rock underneath.

-Igneous and Metamorphic rocks eroded and formed sharp peaks.

Anticlines:

Folds that have the oldest rock in the core or middle, and the youngest rocks on the outside layers.

Synclines:

Folds that have the youngest rock layers on the inside and the oldest rock layers on the outside.