Volcanoes

Lab 5

Concepts Location of active volcanoes

Volcanism 3 categories Viscosity

5 types of extrusive volcanism Examples of each

3 types of lava flows

Dangers of volcanic eruptions

What do you notice about their locations?

Volcanism Definition: the origin and movement of magma

Three categories Extrusive: magma is expelled onto surface Intrusive: magma solidifies in the shallow crust near the

surface. Can be exposed after weathering. Plutonic: magma solidifies deep inside the crust.

Viscosity: The ability for lava to flow. Reflective of the amount of silica present in the magma.

LOW silica = LOW viscosity = nonexplosive HIGH silica = HIGH viscosity = explosive

VolcanismExtrusive Examples

Mt. Fuji, JapanMt. Shasta, CA

VolcanismIntrusive Examples

Right: Stone Mountain, GABelow: Devil’s Tower, WY

VolcanismPlutonic Examples

5 Types of Extrusive Volcanism1. Shield Volcano Central vent allows

magma from chamber to spill out, slowly building the volcano in layers.

Produces wide, gently sloping mountains

Best example: Hawai’ian volcanoes (right: Mauna Loa)

“Stratovolcano” Central vent allows

magma to come up from chamber below

Produces symmetrical, steep-sloped mountains

Most “explosive” type of volcano

Examples: Mt Fuji,Mt Shasta, Mt St Helens

5 Types of Extrusive Volcanism2. Composite Volcano

5 Types of Extrusive Volcanism2. Composite Volcano example: Mt St Helens in 1980

5 Types of Extrusive Volcanism3. Caldera Volcano Formed when the upper part of a

volcano collapses The magma chamber below is (partially or

completely) emptied after an eruption The emptied magma chamber can no

longer support the weight of the overlying rock

The overlying rock collapses into itself, forming a circular basin

Volcanic activity can continue if there is still magma in the chamber below

Example: Crater Lake, OR

5 Types of Extrusive Volcanism3. Caldera Volcano example: Crater Lake, OR

Crater Lake was formed after Mt Mazama (a stratovolcano) eruptedand collapsed back in on itself.

Smallest mountain formation of all volcanic landform types

Cone-shaped peaks build up from small, solid particles, ejected into air by small volcanic vent

Generally <1,500’ high Example: Wizard Island

5 Types of Extrusive Volcanism4. Cinder Cones

5 Types of Extrusive Volcanism4. Cinder Cone example: Wizard Island in Crater Lake, OR

5 Types of Extrusive Volcanism5. Lava Dome “Plug Dome” High-silica lava exits from

a vent. Due to its high viscosity (doesn’t flow very fast or far), it builds up into a dome.

Effectively “plugs” the main vent. Can still emit ash, gases, and even lava.

Example: Lava Dome in Mt St Helen’s crater.

3 Types of Lava Flows

’A’a “Clinky” Blocky, choppy lava flows that does not flow well over land

Pahoehoe “Smooth, unbroken lava” Ropy surface

Pillow Lava Lava emerges from underwater volcanic vents Lava cools & crusts when it hits colder water When crust fractures, lava oozes out and creates billowing

pillows

Pahoehoe

’A’a

Pillow Lava

Dangers of Volcanic Eruptions Burning Hot Lava Earthquakes, Landslides and Tsunamis

These are often related – an earthquake might jar some land loose, resulting in a landslide. The earthquake may set off the tsunami. Also, if the landslide falls into the ocean, can trigger a tsunami.

Mudslides (“Lahars”) Ash Fallout Pyroclastic Flow (“nuée ardente”)

Dangers of Volcanic EruptionsMudslide (Lahar) examples

Mt. Pinatubo, Philippines1991 eruption

Mt. St. Helens, WA1980 eruption

Dangers of Volcanic EruptionsAsh fallout example: Mt. Pinatubo, Philippines 1991 eruption

Dangers of Volcanic EruptionsAsh fallout example: Mt. St. Helens 1980 eruption

Hot gases, ash, rock that become a “fluid cloud” that move down the side of the volcano. Can travel great distances.

“nuée ardente”: French for “glowing cloud”

Dangers of Volcanic EruptionsPyroclastic flow example: Mt St Helens 1980 eruption