Environmental Science Test 3 Terms

Mt. St. Helens

May 18th, 1980. Active stratovolcano in the Cascade Range of southwestern Washington that erupted.

Effects from Mt. St. Helen

Ash spread out everywhere, mudslides, widespread destruction of forests and homes.

2005 reactivation (Mt. St. Helens), know that there was some reactivation that occurred.

December 26, 2005. Activity in 2005 involved the continued growth of a new lava dome inside the crater left by 1980 eruption with some notable explosive events. 

Mt. Pinatubo, 1991

Philippines, second largest volcano eruption of the 20th century. Produced hot ash avalanches, mud flows, and a large ash cloud.

What violence of eruption depends on

Viscosity, Which depends on:

1. Composition (what the melt is made of)

2. Temperature

3. % of dissolved gases in the melt

Granitic Magmas

More viscous, 70%+ silica, short thick flows, too thick for violent explosions.

Basaltic Magmas

Less viscous, 50% silica, longer more fluid flows.

Andesitic Magma

In between granitic and basaltic magma.

Which component of magmas tends to be the most responsible for it explosiveness

Gases in lava flows.

What’s extruded in a volcanic eruption

Lava flows, Gases, Pyroclastics.

Pahoehoe

Higher temperature, more liquid, smooth surface.

Aa

Lower temperature, clumpy, thicker flow.

Gases

About 1 to 5% CO2, H2O, Sulfur, Other gases.

Pyroclastics

-

Ash

Fine-grained material.

Lapilli

Rounded, pea-sized pieces, new.

Pumice

Rains down from volcanoes. Frothy, light rock.

Cinders

Similar to papilla, same size, more jagged, old.

Blocks

Rock sized pieces, comes out solid.

Bombs

Comes out liquid.

Shield Volcanoes

All liquid lava flow. EX: Mauna Loa (Hawaii).

Cinder Cones

All solid lava flows. EX: Sunset Crater (Arizona).

Composite Cones

Liquid and solid lava flow. EX: Mt. Rainier (Washington).