Chapter 5: Volcanoes

Question 1

What are volcanoes?

Answer 1

Hill or mountain that forms around a vent where lava or pyroclastic materials are ejected

Question 2

What is volcanism?

Answer 2

The processes related to rise and discharge of magma

Ex. Fissure eruptions

Question 3

What are Volcanic gases?

Answer 3

Small part of magma that are primarily water. Do not harm humans

Question 4

What are the different kinds of lava flows?

Answer 4

Aa lava: angular blocks and fragments

Pahoehoe: smooth rooy surface

Columnar joints: form when lava flows, cools, and contracts

Question 5

What are the pyroclastic materials?

Answer 5

Solid magma fragments that are explosively ejected by volcanoes

Ash<2mm diameter (small sand grains)

Lipilli 2-64mm

Bombs: partially molten, >64mm

Blocks: solid, >64mm

Question 6

What is ash falls?

Answer 6

Settles out of the atmosphere

Turbulent clouds of ash and gas that travel close to the surface during pyroclastic materials

Question 7

Draw what a conduit, crater, caldera are.

Answer 7

Conduit is the chamber leading to the top of the volcano

Crater is the depression at the summit

Caldera is a large depression that forms when the summit collapses into the magma chamber following an eruption

Question 8

What are some characteristics of a shield volcano?

Answer 8

Gentle slope

Largely composed of basalt with some mafic proclastsb

Usually non explosive

ex. Hawaii

Question 9

What are some characteristics of a cinder come volcano?

Answer 9

Consists of cinders and other pyroclastic materials

Accumulate as steep-slope cones that rarely exceed 400 m High

ex. Wizard island inside of crater lake

Question 10

What are some characteristics of a composite (stratavolcano)?

Answer 10

Composed of layers of lava flows, pyroclastic debris and volcanic mud flows

Explosive

Most have intermediate compositions

ex. Mt. St. Helens

Question 11

What are some characteristics of lava domes?

Answer 11

Form when viscous, usually felsic or intermediate, lavas are forced up through the conduits of some volcanoes.

Can erupt explosively and commonly eject núee ardentes (hot clouds of pyroclastic materials)

Question 12

What are super volcanoes?

Answer 12

Erupt hundreds of square km of material and produce huge calderas

Non have erupted in recorded history
3 have erupted in Yellowstone in the past 3 million years

Possibly caused my a mantle plume

Question 13

What is a basalt plateau?

Answer 13

Fluid mafic lava erupts from long fissures (not vents)

Made up of numerous overlapping basalt- lava flows

ex. Columbia river

Question 14

What are pyroclastic sheet deposits?

Answer 14

Huge sheet-like eruptions of pyroclastic materials, especially ash

Cover large areas when erupted from fissures during caldera formation

Question 15

What are the zones of volcanoes

Answer 15

Circum-pacific belt “ring of fire”
60% of volcanoes

Mediterranean belt
20%

Mid-ocean ridges

Question 16

Explain Alaska’s volcanoes

Answer 16

Stretch from the mainland to the Aleutian Islands

Mostly composite
Some with huge calderas

Extremely active with huge explosions

Question 17

Explain the cascade range

Answer 17

Mostly composite

Has 2 shield and lots of cinder cones

Result from the subduction of the Juan de Fuca

Question 18

Explain volcanic activity at divergent plate boundaries

Answer 18

Volcanic activity near or at mid-ocean ridges is mainly submarine

In a few places such as island, occurs above sea level

Form mafic shield volcanoes

Question 19

Explain volcanic activity at convergent plate boundaries

Answer 19

The volcanism in the circum pacific and Mediterranean belts results from subduction

Magmas are produced by the partial melting of subducted plate

Question 20

How large is an eruption and how long do they last?

Answer 20

Volcanic explosivity index (VEI)
Eruption size indicator
Ranges from 0-8
Measures the explosive intensity of an eruption using: volume of material erupted, eruption cloud height

Eruption duration varies

Question 21

Is it possible to forecast eruption?

Answer 21

Monitoring volcanoes helps geologists to forecast imminent eruptions:
Recording and analyzing both physical and chemical changes at volcanoes
Tiltmeters and geometers are used to detect change of slope, elevation, and shape of the volcanoes

Monitoring involves recording and analyzing both physical and chemical changes at volcanoes
Siesmeters detect harmonic tremors