Lab 4: Volcanos and Volcanic Hazards

Magma

Molten rock beneath the Earth's surface.

Lava

Molten rock that has erupted onto the Earth's surface.

Viscosity

Resistance to flow (how "thick" or "sticky" a liquid is).

High Silica Content

Leads to high viscosity and less flow; typically lighter-colored rocks.

Low Silica Content

Leads to low viscosity and more flow (runny); typically darker-colored rocks.

Shield Volcano

Broad, low-profile volcano formed by fluid mafic lava (Example: Big Island, Hawaii).

Composite Volcano

Tall, cone-shaped volcano formed by viscous magma and explosive eruptions.

Pyroclastic Flow

A fast-moving, "scary" cloud of extremely hot ash and air.

Aphanitic

Igneous texture with microscopic crystals; cooled quickly at the surface.

Phaneritic

Igneous texture with visible crystals; cooled slowly underground.

Diorite

An intermediate igneous rock that is speckled "black and white" (salt and pepper appearance).

Scoria

A dark, vesicular (holy) rock that looks "scorched" or burnt.

Pumice

A light-colored, frothy volcanic rock that often floats in water.

Obsidian

Volcanic glass formed by extremely rapid cooling.

Basalt

A dark, fine-grained (aphanitic) mafic volcanic rock.

Granite

A light-colored, coarse-grained (phaneritic) felsic plutonic rock.

Gabbro

Mafic rock with phaneritic (visible) crystals; did not erupt

Rhyolite

Felsic rock with aphanitic (microscopic) crystals; erupted from a volcano

Andesite

Intermediate rock with aphanitic crystals; erupted from a volcano.

Felsic Composition

High silica, high viscosity, light-colored (pink/light) minerals

Intermediate Composition

Medium silica, "salt and pepper" or gray coloration

Mafic Composition

Low silica, low viscosity, dark gray or black minerals

Viscosity Rule: more, more, less

More silica = More viscous = Less flow

Viscosity Rule: less, less, more

Less silica = Less viscous = More flow