Midterm Study Guide 4

Question 1

Name four hazards associated with volcanoes.

Answer 1

• Lahars
• Volcanic gas
• Pyroclastic flows
• Lava flows

Question 2

What causes the difference in eruptive style between an Andean and a hotspot volcano?

Answer 2

Silica content

• High silica-high viscosity–explosive–Andean
• Low silica -effusive–Hotspot

Question 3

What is the relationship between a large igneous province and Hawaii?

Answer 3

Recent imaging of the region below known hot spots (e.g., Yellowstone and Hawaii) using seismic-wave tomography has produced mounting evidence that supports relatively narrow, deep-origin, convective plumes that are limited in region compared to the large-scale plate tectonic circulation in which they are imbedded. Images reveal continuous, but torturous vertical paths with varying quantities of elevated temperature material, particularly at elevations where crystallographic transformations are predicted to occur

Question 4

What is the difference between Pahoehoe and Aa?

Answer 4

Pahoehoe is faster moving lava and Aa is slower moving lava.
Pahoehoe is smooth and ropey while AA is chunky and rough.
The steeper the slope the more likely Aa lava will be present. Aa has higher viscosity than Pahoehoe.

Question 5

What types of plate boundaries show volcanism?

Answer 5

Mid-ocean ridges and subduction zones.

Question 6

Why is there a bend in the Hawaii-Emperor seamount chain?

Answer 6

Due to the permanent location of the hot spot creating the Hawaii- Emperor seamount chain, we are able to conclude that the bend created is due to the movement of the plate that sits on top of it. Plate has moved north west.

Question 7

Name two effects that increase the likelihood of melting of a rock at constant temperature?

Answer 7

1. Decompression at divergent plates: if something rises quickly enough that it doesn’t loose its high temp but experiences a decrease in pressure, it will decompress from a solid to a liquid. Happens at spreading centers/mid ocean ridges when the mantle convects.
2. Lowering the liquidus (boundary at which a solid will melt) at subduction zones: when an oceanic plate is subducted, the sediments of the plate release water which lowers the liquidus of the rocks that it touches. Lowering the liquidus makes the current rocks’ temperature fall within the liquid portion of the phase diagram, allowing it to melt. Melting the rock turns it into magma and so on.

Question 8

How is a lahar generated?

Answer 8

1) from debris avalanches that contain water from snow and ice which, when released, mixes with loose debris to form a lahar
2) from pyroclastic flows and surges which release water that mixes with debris
3) from pyroclastic flows which dilute themselves with river water as they travel downslope
4) from natural dam failure (i.e. a lava flow dam or crater lake)
5) from rainfall on loose material such as ash. Lahars that contain 20 to 60 percent sediment are usually very turbulent. Lahars that contain greater than 80 percent sediment usually flow more smoothly (laminar flow).

Question 9

What is a typical eruptive temperature of lava?

Answer 9

Temperature for lava is between 700 degrees to 1200 degrees (celcius)

Question 10

Is the mantle molten?

Answer 10

No. It’s a layer of silicate rocks that are weak and ductile enough for the layer to flow very slowly under heat convection (makes it look as if it’s a slow moving liquid, which is why plates drift).

Question 11

hotspot

Answer 11

A portion of the Earth’s surface that may be far from tectonic plate boundaries and that experiences volcanism due to a rising mantle plume or some other cause.

Question 12

Andesite

Answer 12

a dark, fine-grained, brown or grayish volcanic rock that is intermediate in composition between rhyolite and basalt

Question 13

nuee ardante

Answer 13

• french for “glowing cloud”

- incandescent cloud of gas, ash, and lava fragments ejected from a volcano, typically as part of a pyroclastic flow

Question 14

Pahoehoe

Answer 14

basaltic lava forming smooth undulating or ropy masses.

Question 15

pyroclastic flow

Answer 15

a dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing downslope at great speed

Question 16

caldera

Answer 16

a large volcanic crater, typically one formed by a major eruption leading to the collapse of the mouth of the volcano

Question 17

felsic

Answer 17

of, relating to, or denoting a group of light-colored minerals including feldspar, feldspathoids, quartz, and muscovite

Question 18

igneous rock

Answer 18

• formed through the cooling and solidification of
  magma or lava
• E.g. Basalt, gabbro, rhyolite, granite, etc.

Question 19

plume

Answer 19

a localized column of hot magma rising by convection in the mantle, believed to cause volcanic activity in hot spots, such as the Hawaiian Islands, away from plate margins.

Question 20

large igneous province

Answer 20

A large igneous province (LIP) is an extremely large accumulation of igneous rocks—intrusive, extrusive (smaller in grain size compared to intrusive), or both—in the earth’s crust

Question 21

rhyolite

Answer 21

a pale fine-grained volcanic rock of granitic composition, typically porphyritic in texture

Question 22

lahar

Answer 22

Typically lava that will flow down from a volcano. Usually just flowing with/into an already paved river path. Extremely dangerous, because hot lava flow will destroy everything in its path and secondly when it cools it will harden and be difficult to remove.

Question 23

Aa

Answer 23

basaltic lava forming very rough jagged masses with a light frothy texture

Question 24

tephra

Answer 24

rock fragments and particles ejected by a volcanic eruption

Question 25

Plinian

Answer 25

relating to or denoting a type of volcanic eruption in which a narrow stream of gas and ash is violently ejected from a vent to a height of several miles.

Question 26

lava

Answer 26

an intrusion of igneous rock cutting across existing strata

Question 27

tsunami

Answer 27

a long high sea wave caused by an earthquake, submarine landslide, or other disturbance.

Question 28

viscosity

Answer 28

the state of being thick, sticky, and semifluid in consistency, due to internal friction.

Question 29

mafic

Answer 29

relating to, denoting, or containing a group of dark-colored, mainly ferromagnesian minerals such as pyroxene and olivine.

Question 30

basalt

Answer 30

a dark, fine-grained volcanic rock that sometimes displays a columnar structure. It is typically composed largely of plagioclase with pyroxene and olivine.

Question 31

granite

Answer 31

a very hard, granular, crystalline, igneous rock consisting mainly of quartz, mica, and feldspar and often used as a building stone

Question 32

peridotite

Answer 32

a dense, coarse-grained plutonic rock containing a large amount of olivine, believed to be the main constituent of the earth’s mantle.