Volcanoes

Question 1

Shield Volcanoes

Answer 1

Basalt lavas are relatively silica-poor (45-50% SiO2) and as a result, are less viscous. This flowing lava forms broad, shield-shaped volcanoes with large diameters and low heights.

Lava will often erupt from vents or flanks of volcanoes. Each layer of rock will represent many hundreds of thin flows of basic lava.

Question 2

Volcanic Domes

Answer 2

Consists of silica rich (70%) lave (usually rhyolite and andesite). These flow less readily, these lava’s pile up close to the vent and build high peaks. They are associated with violent eruptions, as the dome will block the vent and trap gas. The vent may also be filled with volcanic debris.

Question 3

Stratovolcano

Answer 3

Composite volcanoes comprise alternating pyroclastic layers and lava flows. They can grow both domes and cinder cones with alternating slopes. They will have intermittent eruptions over a long-time span.

The lava is mostly gas-laden and andesitic.
The magma can accumulate in significant reservoirs over subduction zones.

Question 4

Example of Shield Volcanoes

Answer 4

Hawaii (Mauna Loa, Kilauea, Mauna Kea) and Olympus Mons Shield Volcano on Mars

Question 5

Example of Volcanic Dome Volcanoes

Answer 5

Mount St.Helens

Question 6

Example of a Cinder-cone volcano

Answer 6

Paricutin volcano in Mexico, Cerro Negro in Nicaragua.

Question 7

Examples of Strata Volcanoes

Answer 7

Mount Fuji and Mount Vesuvius

Question 8

Cinder-cone Volcanoes

Answer 8

Formed entirely out of pyroclastic materials that accumulate near the volcanic vent. Pyroclastic activity is more viscous, silicic magmas, and falls symmetrically to form a cone shape.

They have steep sides, with fragments falling from the summit and smaller fragments falling from the base.

They are small with a short activity.

Question 9

Caldera

Answer 9

Result when a violent eruption empties a volcano’s magma chamber, which then cannot support the overlying rock. It collapses, leaving a large, steep-walled basin.

Can be up to 50 km in diameter.

Question 10

Resurgent Calderas

Answer 10

Calderas with continuing volcanic activity

Question 11

Example of a resurgent caldera

Answer 11

Yellowstone and Crater lake in Oregon

Question 12

Formation of Crater Lake in Oregon

Answer 12

1. Fresh magma filled the magma chamber of Mount Mazama and triggers a volcanic reaction.
2. The eruption continues and the magma chamber becomes partially depleted.
3. The mountain summit collapses into the empty chamber, forming a caldera. Large pyroclastic flows accompany the collapse, blanketing the caldera, and a surrounding area of hundreds of square kilometers.
4. A lake forms in the caldera. As the residual magma in the chamber cools, minor eruptive activity continues in the form of hot springs and gas emissions. A small volcanic cone forms in the caldera.

Question 13

Pyroclastic Flows

Answer 13

• Mixtures of hot gases, ash, and rocks form a superheated gas and dense current.
• generated during violent volcanic eruptions where molten material cools before falling to earth
• different from central eruptions

Question 14

Example of Pyroclastic flow

Answer 14

Mount Vesuvius in 79 AD in Pompeii

Question 15

Phreatic Explosion in the Pacific

Answer 15

The result of excessive subsurface pressure due to steam buildup (similar to an exploding boiler). Volcanic islands are susceptible to seawater seepage, and when magma meets water it turns into superheated steam.

Question 16

Example of a Phreatic explosion

Answer 16

island of Krakatoa in Indonesia

Question 17

Fissure Eruptions

Answer 17

Highly fluid basaltic lava may flow out of fissures, rather than a single vent. The highly fluid basalt erupting from fissures forms widespread layers rather than mountains.

Question 18

Large igneous province

Answer 18

Large fissure eruptions on land

Question 19

The most geographically important fissure eruption is ___

Answer 19

occurring at the spreading centers of mid-ocean ridges. The majority of volcanic rock is produced from fissure eruptions.

Question 20

Flood Basalts

Answer 20

Successive eruptions on flat surfaces produce plateaus characterized by layered flood basins.

Question 21

Example of a large igneous province/ flood basin

Answer 21

Laki eruption in Iceland killing 1/5 of the population

Question 22

Siberian Traps

Answer 22

Flood basalts cover an area twice the size of Alaska. They erupted 250 million ya and are implicated in a global mass extinction event.

Question 23

Diatremes

Answer 23

Eruptions originating from the asthenosphere. They form by:

1. Gas-charged magma from deep in the mantle forcing its way upward from the lithosphere
2. Magma breaks off and carries crust and mantle fragments as it explodes
3. After the eruption, the feeder channel forms a diatreme of solidified magma and rock fragments called breccia
4. Softer sediments of cone and surface erode, leaving the diatreme core

Question 24

Kimberlites

Answer 24

A form of diatreme and a volcanic form of peridotite (a rock made of mostly olivine). They contain many fragments, such as diamonds, and form in mines in South Africa and Canada.

Question 25

Example of a diatreme

Answer 25

Shiprock, New Mexico

Question 26

Distribution of Volcanoes based on convergent, divergent boundaries or interplate

Answer 26

80% convergent, 15% divergent, and 5% interplate

Question 27

Ocean volcanoes composition

Answer 27

Basaltic

Question 28

Hot Spot volcano composition

Answer 28

Basaltic (like Hawaii)

Question 29

Mid-ocean Ridge volcano composition

Answer 29

Basaltic

Question 30

ocean-continent volcano composition

Answer 30

basalts from the mantle, felsic content from the crust, and remelted materials from the subducting crust

Question 31

Divergent Margins

Answer 31

Basaltic magma moves from the asthenosphere and is forced upwards through vents. The melt overflows and forms ocean ridges.

Question 32

3 km3 of basic lava erupts annually at

Answer 32

mid-ocean ridges

Question 33

In the past ___ years, enough magma has been released to form today’s present ocean crust.

Answer 33

200 million

Question 34

Convergent Margins

Answer 34

Magma arises due to subduction and is more varied in composition. Subducted water induces melting in the mantle above it producing basaltic to andesitic magma in ocean-ocean convergence. In ocean-continent convergence, rising magma causes melting of crust above it forming andesitic to rhyolitic magmas.

Question 35

Interplate Zones

Answer 35

Hot spots and deep magmatic mantle plumes rise to the surface from lower pressures and produce melting of the asthenosphere and the eruption of basaltic lava. Hot spots are fixed in the mantle and leave a trail of activity over the plate.

Question 36

Hazards of Volcanic eruptions

Answer 36

Eruption cloud and eruption column, bombs, pyroclastic flows, ashfall, landslide (debris avalanche), fumaroles (steaming groundwater), acid rain, lava flow, lahar (mud and debris flow)

Question 37

Lahar

Answer 37

mudflow from melting snow

Question 38

Ashfall

Answer 38

pyroclastic deposition

Question 39

Gases emitted during volcanic activity

Answer 39

H2O, H2S, CO2, HCl

Question 40

Example of pyroclastic ashfall

Answer 40

Mount St.Halens across North America

Question 41

Climatic effects of volcanic dust

Answer 41

1. Dust can block sunlight, lowering global temperatures in a manner called “nuclear winter”.
2. Sulfur-rich gases induce sulfuric acid rains and aggravate ozone depletion.