Volcanic Activity

Question 1

What are the two factors that control volcanic eruptions?

Answer 1

Viscosity & Gas Content

Question 2

What is Viscosity?

Answer 2

A magma’s silica (Si) content determines viscosity

Viscosity controls how easily magma can erupt

Question 3

Low Silica=

Answer 3

Runny Rivers

Question 4

High Silica=

Answer 4

Sticky Mounds

Question 5

What is Gas Content?

Answer 5

Magma gas can be low or high, depending on source

High gas content gives magma its ‘explosive power’

Question 6

Lava flow Eruptions are characterized by there?

Answer 6

low viscosity and low gas content,

runny magma remains fluid and flows downhill ,

usually gentle, fairly safe, can be enormous

Question 7

WHAT IS Pahoehoe?

Answer 7

Hot flow with a ropy texture

Question 8

As lava cools, it breaks up into:

Answer 8

jagged aa texture

Question 9

Underwater, flow make round blobs=

Answer 9

Pillow Lava texture

Question 10

Pyroclastic Eruptions are characterized by there?

Answer 10

Medium to High Viscosity & Gas Content

Sticky Magma explodes into small solid bits as it erupts

always violent, often destructive, can erupt up or sideways

Question 11

The 2 types of Pyroclastic Eruptions are?

Answer 11

Ash Clouds and Nuee Ardentes

Question 12

Ash Clouds are characterized by?

Answer 12

Very fine dust with some larger chunks

Cold ash- turns into TUFF
Hot ash- makes WELDED TUFF

Question 13

What is Nuee Ardentes?

Answer 13

glowing cloud of hot ash and gas. Hugs the ground like an avalanche

Question 14

Olivine Crystals settle _________________

Answer 14

to the bottom, making ultramafic magma

Question 15

Mantle magma rises __________________

Answer 15

through the cracks between plates.

Question 16

Mafic Volcanoes are characterized by there?

Answer 16

Largest but safest

“gentle giants” or “Shield Volcanos”

have a gentle slope

Question 17

Intermediate magma forms ___________

Answer 17

where ocean floor partially melts, making new

continents (recycling old ocean into new continent)

Question 18

Intermediate Volcanos are characterized by there?

Answer 18

Most dangerous

Alternating ash and lava flows

steep & can blow itself up

STRATOVOLCANO/”Sneaky Serial Killers”

Question 19

When continental rocks melt __________

Answer 19

they distill out an even lighter magma very rich in silica

Question 20

Felsic Magma is

Answer 20

very sticky

Question 21

Felsic Volcanoes are characterized by there?

Answer 21

Smallest

shortest lived

Very Sticky lava

makes Nuee Ardentes

Question 22

What do Nuee Ardentes make?

Answer 22

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