Do you know… where volcanoes are found? what kinds of things come out of volcanoes? why all volcanoes are not the same?

Anatomy of a Volcano

Where in the U.S.? Hawaiian Islands Cascades Yellowstone national park Mammoth lakes, ca Aleutian islands & alaskan peninsula

Volcanoes form in 3 types of areas

Divergent Boundaries Magma rises up through the rift, creating a volcano. Much of this happens under the ocean surface, but…

Sometimes the volcano is tall enough to peek-out from the ocean surface, creating a Land of Fire and Ice volcanic island.

Iceland 2010 Eruption Eyjafjallajokull Volcano

Glacial melt due to Volcano

Ash Plume over the North Atlantic Ocean

Convergent Boundaries When tectonic plates collide, the oceanic plate subducts and melts. Because magma is less dense than the surrounding rock, it rises to the surface.

Trenches also form at the subduction zone This can form volcanoes… on land and on the ocean floor Krakatau, Java Cleveland, Alaska

Most of these convergent plate volcanoes are located in the Ring of Fire

Ring of Fire!

Hot Spots Hot spot volcanoes form in the middle of tectonic plates. There are spots in the asthenosphere that are unusually hot. The earth’s crust is in constant motion,but the hot spot is fixed in place. A new volcano is formed on the crust that is directly over the hot spot

Two types of eruptions: 1. Explosive 2. Non-Explosive (Quiet) Pyroclastic Flow (clouds of gas and ash that race down the sides of a volcano) during an explosive volcanic eruptions Can be 2,000 degrees F

Lots of silica- glassy, light Lots of gas (explosive eruptions) Slow moving Usually on land Little silica- dark Little gas (effusive eruptions) Fast moving Usually in ocean

Lava of low viscosity with long thin flows Creates pahoehoe, aa, columnar jointing and lava tubes Columnar jointingLava tube

“ropey”, wrinkled Jagged chunks from rapid cooling Under water Outer shell cools, liquid center

Pahoehoe Lava

Aa Lava

Intermediate lava (higher Si and higher viscosity than basaltic) with a lumpy flow. Cools as it moves, surface breaks up to look like a rubble pile.

Lava with highest Silica, and is the most viscous MOST DANGEROUS Often produces a Nuee Ardente Glowing gas and ash cloud

“pyro” = fire and “clastic” = rock This is a general term for igneous rock fragments ejected from a volcano. 2,000 degrees F Volcanic avalanche The debris is classified based on size and if consolidated or not.

Solid fragments from volcanoes Biggest Smallest Volcanic blocks Volcanic bombs Lapilli Volcanic ash Volcanic dust

Ash

Lapilli

Blocks and Bombs

Up to 90% of a magma’s composition may be gas! Water vapor Carbon dioxide Sulfur dioxide Hydrogen sulfide

Lahar = meltwater and volcanic ash flows Hot Springs = may be lukewarm to boiling Geysers = periodic hot water and steam eruptions Igneous Intrusions = magma hardens in between rock layers Geothermal Energy = Iceland!

Layers of lava Gently sloping sides Effusive eruptions Usually basalt Ex) Hawaii

Layers of tephra Steep but not very tall From explosive eruptions Short lived Ex) Pericutin, Mexico

Layers of tephra and lava Grows very tall Effusive/explosive eruptions Ex) Mount St. Helens

Thick pasty rhyolitic lavas can “plug” existing volcanic vents Lava plug

Adds new rock to Earth’s surface – land building Creates very fertile soils Provides clues to what is happening inside the Earth

Geologists look for: Changes in shape (bulges) –Tilt of mountain changes as magma pushes upward Changes in heat flow (rock temp., melted snow) Increase gas and steam emissions Earthquake activity

Evacuation! Create danger assessment maps Divert lava flows with high explosives, building dams, or spraying with cold seawater

Igneous Formations / Intrusions Columnar Jointing

Sill – horizontal layer of cooled igneous rock

Dike – vertical column of cooled magma

Laccolith – dome shaped rock from cooled magma

Batholith – large body of cooled magma (40 sq. miles)

Caldera – empty magma chamber Crater Lake, Oregon