Volcanoes Objectives (Ch. 9)

Question 1

What is the difference between magma and lava?

Answer 1

magma - below the surface

lava - above the surface

Question 2

What determines the kind of eruption a volcano will have? What does that depend on?

Answer 2

the mobility or viscosity of its magma, which is determined by its composition (esp. its silica, SiO2 content) and temperature (hotter=more fluid)

Question 3

Compare and contrast basaltic and rhyolytic (felsic) magmas.
-Rank order the properties of each type of magma (Table “Properties of Magmas”)

Answer 3

see first page of volcanoes notes

Question 4

Name some gases commonly emitted by volcanoes.

Answer 4

water vapor
carbon dioxide
sulfur dioxide

Question 5

What are pyroclastics? List and briefly describe some pyroclastics based on size.

Answer 5

solids

welded tuff - rock from hot ash fusing (small, 64 mm

Question 6

What is the difference between pumice and scoria? What type of volcano would produce each?

Answer 6

Pumice is a vesicular rock from a felsic or andesitic magma; light tan to gray; composite
Scoria is a vesicular rock from a basaltic magma; black to reddish-brown; shield and cinder

Question 7

What is the difference in behavior and silica composition of andesitic and basaltic lavas?

Answer 7

Andesitic: high in silica; dissolved gases do not escape easily, lave plugs throat of volcano, pressure builds up until a violent eruption takes place; very viscous; produce no lava flows or very thick flows that move very slowly
Basaltic: low in silica; dissolved gases escape easily; produce thin, “fast” flows; aa flow - rough, rubbly appearance; pahoehoe flow - “smooth” “ropy” surface

Question 8

What is the difference between a pahoehoe and an aa lava flow?

Answer 8

aa - thicker, cooler, slower

pahoehoe - thinner, hotter, faster; can flow long distances; may change into aa as it cools

Question 9

What kind of magmas would produce an eruption column or a lava fountain in an eruption?

Answer 9

Eruption column is produced from a highly viscous, silica rich magma with a lot of dissolved gas.
Lava fountain is produced from a fluid basaltic magma.

Question 10

What are lava tubes and how are they formed?

Answer 10

develop in fluid, basaltic (pahoehoe) flows; the surface of a lava flow cools and hardens, the hot interior continues to flow and drains out at the end of the eruption

Question 11

Which type of volcano would lava tubes be associated with?

Answer 11

shield

Question 12

What is a volcanic pipe?

What may be found in some volcanic pipes?

Answer 12

A vertical conduit below a volcano through which magma has passed and that has become filled with solidified magma, volcanic breccia, and fragments of older rock.

Question 13

Compare and contrast the three types of volcanoes. Name examples of each.

Answer 13

Cinder:

mainly basaltic lapilli; usually

Question 14

What are pyroclastic flows and lahars? What type of volcano produces them?

Answer 14

Pyroclastic flow is a hot, dense cloud of ash and gas that race down steep volcanic slopes (can be >100 mph) and knock over, incinerate, or asphyxiate everything in its path; most are from the collapse of a tall eruption column; extremely destructive and pose the greatest threat to life; composite
Lahars are mudflows; it is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley; second most dangerous volcanic threat; esp. from volcanoes w/ glaciers; composite

Question 15

Name and describe other common volcanic hazards.

Answer 15

fumarole: secondary vents on the sides of a volcano that emit only gases
ash and pyroclastics
gases - sulfur dioxide can kill or cause lung disease
tsunami
global cooling

Question 16

What is the difference between a crater and a caldera?

Answer 16

A crater is a depression at the top of the cone, connected via a “pipe” or “vent” to a magma chamber below the surface; may extend more than 120 miles into the Earth; may bring material from great depths to the surface.
A caldera is a very large, roughly circular depression; > 1 km diameter; usually represents the remains of a volcano that has collapsed.

Question 17

Compare and contrast the three types of calderas. Name examples of each.

Answer 17

Crater Lake: from collapse of large composite volcano after explosive eruption
Hawaiian: from the collapse of the top of a shield volcano when the magma chamber drains; looks like a huge, flat-bottomed pit
Yellowstone: form after the discharge of enormous volumes of pumice and ash from a monstrous magma chamber when the chamber roof collapses; supervolcano eruptions; these are the largest volcanic structures on Earth; depressions are difficult to identify on the ground

Question 18

What is a volcanic neck?

Answer 18

the eroded pipe that remains after the surrounding volcano has eroded away

Question 19

What are fissure eruptions and how are they different from normal volcanic eruptions?

Answer 19

a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is often a few meters wide and may be many kilometers long.

Question 20

Where is the major flood basalt in the U.S. located?

Answer 20

Columbia Plateau, covers much of WA, OR, and ID

Question 21

Describe the general zones of volcanism of the world. Name examples of volcanoes in each zone. What is the Ring of Fire? Are volcanic eruptions in the Ring of Fire generally quiet or violent?

Answer 21

1. Volcanoes at Convergent Boundaries
   - more than 60% of the world’s volcanoes are in the Circum-pacific belt; found next to ocean trenches; “Ring of Fire” has most of world’s active volcanoes (mostly composite cones of andesitic composition); about 20% in Mediterranean; Aleutians, Andes, Cascades, Tonga
2. Volcanoes at Divergent Boundaries
   - make up oceanic ridge system
   - greatest volume of volcanic rock is produced from basaltic magma on the ocean floor
   - volcanoes along rift zones
   - Iceland, Kilimanjaro
3. Intraplate
   - located over a “hot spot”
   - Hawaii; Yellowstone