GEOL 3310 Test 2 (CH 9, 2, 4, 5)

Shield volcano characteristics

1. largest 2. almost exclusively basalt 3. gentle slope (2-10 degrees) 5. from hotspot volcanism 6. generates pahoehoe and aa lava

About how many people live near volcanoes?

1/2 billion

How many volcanoes are active in the world today?

500

Mt. St. Helens exploded depositing over _____ of ash over a _____ state area.

540 million tons, 3

California has _____ volcanoes.

66

dissolved gases in Hawaiian eruptions

70% Water Vapor 15% Carbon Dioxide 5% Nitrogen 5% Sulphur Dioxide 5% Chlorine, hydrogen, argon

Ring of Fire

A major belt of volcanoes that rims the Pacific Ocean

Magma

A molten mixture of rock-forming substances, gases, and water from the mantle

cinder cone volcano

A small, steeply sloped volcano that forms from moderately explosive eruptions of pyroclastic material.

composite volcano characteristics

A tall, cone-shaped mountain in which layers of lava alternate with layers of ash and other volcanic materials. Located mostly on the "Ring of Fire".

convergent boundary

A tectonic plate boundary where two plates collide, come together, or crash into each other.

columnar jointing

A type of fracturing that yields roughly hexagonal columns of basalt; columnar joints form when a dike, sill, or lava flow cools.

dormant volcano

A volcano that has erupted sometime in the last several thousand years, but has not erupted in the last few hundreds years.

extinct volcano

A volcano that has not erupted since recorded human records

Lahar

An avalanche of volcanic ash, water and mud down the slopes of a volcano

Eruption of Mount Vesuvius

August 24th, 79 AD

cinder cone volcano example

Capulin, NM and Paricutin, Mexico

Basalt Plateau example

Columbia Plateau

Anatomy of a volcano

Conduit/pipe, vent, crater, caldera, parasitic cones, fumaroles

Volatiles

Dissolved gases in magma that vaporize at surface pressure

Pumice - Igneous

Extrusive Light colored white to grey, dull texture, floats in water, formed from the bubbly froth at the top of lava.

Plutons

Intrusive igneous rock bodies, including batholiths, stocks, sills, and dikes, formed through mountain-building processes and oceanic-oceanic collisions; can be exposed at Earth's surface due to uplift and erosion.

active volcano examples

Kilauca, Hawaii and Mt. St. Helens

extinct volcano example

Kohala, Hawaii

pillow lava

Lava that cools underwater, taking on a distinctive pillow-like shape as it hardens

How is volcanic rock produced along the oceanic ridge system?

Lithosphere pulls apart Less pressure on underlying rocks Partial melting occurs Large quantities of fluid basaltic magma are produced

Lava

Magma that reaches Earth's surface

Caldera Examples

Mt. St. Helens, Crater Lake in Yellowstone

dormant volcano example

Muana Kea, Hawaii

types of lava flows

Pahoehoe and Aa

decompression melting

Partial melting of hot mantle rock when it moves upward and the pressure is reduced to the extent that the melting point drops to the temperature of the body.

volcanic neck example

Ship Rock, New Mexico and Devil's Tower, Wyoming

pyroclastic material

The volcanic rock ejected during an eruption, including ash, pumice, lapilli, cinders, blocks, bombs

Yellowstone Supervolcano

Threat to USA, large hot spot of mantle magma sits beneath yellowstone national park, if it erupts it could be a catastrophe

scoria cone

a glassy, mafic, igneous basaltic rock containing abundant air-filled holes

pyroclastic flow (nuee ardente)

a highly heated mixture, hot gases largely infused with ash fragments produced by composite cones, traveling down the flanks of a volcano or along the surface of the ground at speeds up to 200 km (125 miles) per hour

Calderas

a huge, steep-walled, bowl-shaped depression formed when an empty magma chamber collapses after a volcanic eruption which size exceeds 1 km in diameter

silica

a material found in magma that is formed from the elements oxygen and silicon we will use quartz in this class

volcano conduit

a pipe that carries magma from the magma chamber up through the crust until it reaches the surface

crater

a summit depression greater than 1 km diameter

sill pluton

a tabular concordant pluton resembling buried lava flows and may exhibit columnar joints

dike pluton

a tabular discordant pluton

Lahar Flow

a type of mudflow or debris flow composed of a slurry of pyroclastic material (ash and water) and rocky debris produced mostly by melted glaciers or rain

parasitic cone

a volcanic cone that forms from fissures on the flank of a larger volcano

active volcano

a volcano that is erupting or has erupted in the last few hundred years

The greatest volume of volcanic rock is produced

along the oceanic ridge system.

Basalt Plateaus (flood basalts)

basaltic lava extruded from elongated crustal fractures or fissures and spreads widely to create vast, flat lava plains, sometimes covering 10's or 100's of thousands of square kilometers.

Types of plutons include

batholiths, stocks, sills, dikes, and laccoliths

Crater Lake sits in a _____ with Wizard Island a _____ _____ in it.

caldera, cinder cone

The chain of 17 major olcanoes/mountains in California, Oregon, and Washington State is call the_____

cascade range.

factors that determine the violence of a volcano eruption

composition, temperature, and dissolved gasses in magma

Second amount of volcanoes are located...

confined to the deep ocean basins (basaltic lavas)

Mt. St. Helens with Spirit Lake at its base had been _____ for over 123 years.

dormant

ash

fine, glassy fragments

Columbia River Basalts

flood basalts in NW North America

basaltic lavas are more

fluid

Mt. St. Helens exploded sending a _____ cloud 72,000 ft high.

gas

factors effecting viscosity of magma - composition

high silica - high viscosity (rhyolitic lava) low silica - more fluid (basaltic lava)

fumaroles

holes or cracks serving as escape vents for underground gases

interplate volcanism are

hot spots

Third amount fo volcanoes are located...

in the interiors of continents

thick piles of unconsolidated ash + a hurricane =

lahar

Mt. St. Helens exploded melted snow cap formed a _____ that traveled along the _____ to the northwest of the volcano.

lahar, river drainage system

----- + heat & ash =

lahar.

volcanic bombs

large symmetrical blobs of magma that harden in the air

batholith pluton

largest intrusive body that often occurs in groups, surface exposure is 100+ kilometers and frequently form the cores of mountains

factors effecting viscosity of magma - volatiles

mainly water vapor and carbon dioxide gases expand near the surface provide the force to extrude lava viscous magma produces a more violent eruption

viscosity

measure of a liquid's resistance to flow

Devil's Tower is a _____ of an extinct _____.

neck, volcano

Most volcanoes are located...

on the margins of the ocean basins

hot spot volcanoes

produces a chain of volcanos as in Hawaii, can arise from the ocean floor, can arise on continents, and may arise in the interior of lithospheric plates

What type of event buried Pompeii in steam, gases, and ash-pumice?

pyroclastic

Mt. St. Helens exploded sending a _____ traveling _____ wiping out _____ of the forest.

pyroclastic ash/gas flow, 670 mph, 230 sq mi

What is more dangerous than lava during a volcanic eruption?

pyroclastic flows

Types of Lava: Pahoehoe

resembles braids in ropes

types of Lava: Aa

rough, jagged blocks

Materials associated with volcanic eruptions

see handout

Types of volcanoes

shield, composite, cinder cone, dome

laccolith pluton

similar to a sill, lens shaped mass, arches overlying strata upward

Mt. Baker gets over 65 feet of _____ per year.

snow

volcanic neck

solid igneous core of a volcano left behind after the softer cone has been eroded

divergent plate boundaries

tectonic plates spreading apart, new crust being formed (ex. mid-ocean ridges, rift valleys).

volcanic pipe

the conduit connecting the crater of a volcano with an underlying magma chamber

geothermal gradient

the gradual increase in temperature with depth in the crust

volcanic blocks

the largest pieces of pyroclastic material, are pieces of solid rock erupted from a volcano

volcano vent

the surface opening connected t4o the magma chamber via a pipe

factors effecting viscosity of magma

volatiles, temperature, silica content

Unlike earthquakes, many _____ _____ may be (almost) _____ by geologists.

volcanic eruptions, predicted

What is one of the lures to volcanoes by people?

volcanic rock produces very rich soil

lapilli (cinders)

walnut size

Magma originates

when solid rock, located in the crust and upper mantle, melts and factors that influenced by the Earth's natural temperature increases because of friction in subduction zones, crustal rocks heated during subduction, and rising hot mantle rocks when depth is not sufficient to melt rock at the lower crust and upper mantle