types of volcanoes and hazards II

Question 1

the order basaltic, andesitic and rhyolitic shows increases is?

Answer 1

silica, viscosity, explosivity

Question 2

what makes a volcano volatile?

Answer 2

water, various gasses

Question 3

what are the properties of mafic lava (basalt)?

Answer 3

• low silica = low viscosity (runny)
• gases in magma can easily escape
• less explosive, lava flow dominates (add water, all bets off)
• mafic eruptions most common where magma has the most direct route to surface
• does not produce as much tephra or ash into the air
• lava is spouting !

Question 4

what are the largest mountains on earth?

Answer 4

shield volcanoes

Question 5

how are shield volcanoes made?

Answer 5

• basalt flows are fluid and build up one layer upon another layer over time
• may come out from flank eruptions

Question 6

what are some properties of shield volcanoes?

Answer 6

• low topography
• predominantly build from mafic flows, but can have higher silica eruptions

Question 7

what are the properties of cinder cone volcanoes?

Answer 7

• smaller than shield volcanoes
• formed by basaltic mafic lava that is very gas charged and rises very quickly

Question 8

what are fissure eruptions?

Answer 8

• mafic lava not erupted through a central vent / hole
• cracks that open in the earth and lava fountains out of the cracks
• mid-ocean ridges is where the new crust is formed
• largest eruptions in earth’s history (flood basalts)
• can be extremely large and very intense

Question 9

what are kimberlite eruptions?

Answer 9

• ultramafic
• large gas filled eruption that travels from mantle to surface in a very short period of time (rips a hole in the earth called mars)

Question 10

what are the properties of felsic or intermediate lava?

Answer 10

• high silica = high viscosity (very thick)
• magma gasses cannot easily escape
• can produce very large eruptions
• large amounts of tephra and gas

Question 11

where do stratovolcanoes / composite volcanoes form?

Answer 11

along subduction zones

Question 12

what are some properties of stratovolcanoes?

Answer 12

• white vapor: water
• rock fragments and tephra is grey
• often snow on top of these mountains, meaning lava is immediately interacting with water, which generates large explosions
• produced by alternating layers of lava, tephra, and pyroclastic flow deposits
• classic cone volcanoes !!
• usually eruptions intermediate magma
• major eruptions can destroy

Question 13

how do lava domes form?

Answer 13

• erupting lava is too thick to flow, causing it to pile up and rebuild stratovolcanoes
• lava reaches surface, very viscous, does not flow easily, pushes up, outside breaks and gets pushed around until whole crater is filled with lava domes, and then could potentially go back to forming a beautiful cone

Question 14

how can lava domes collapse?

Answer 14

pyroclastic flows

Question 15

what are calderas?

Answer 15

very large craters or gigantic depressions in the ground; can be very large

Question 16

how are calderas formed?

Answer 16

• by a collapse
• earlier eruptions, big event, drain upper part of magma chamber, ground collapsed, steam explosions, filled by a lake
• formed by very large eruptions

Question 17

what are the seven volcanic hazards?

Answer 17

1. lava flows
2. tephra (ash) fall
3. pyroclastic flows
4. mudflows
5. tsunamis / landslides
6. gas emissions
7. climate change

Question 18

what are lava flows?

Answer 18

large flows limited to fluid magma (ex. basalt), but there can be exceptions

Question 19

what are some characteristics of lava flows?

Answer 19

• slower moving
• virtually impossible to stop

Question 20

what is tephra?

Answer 20

• ash
• significant ash fall is generally limited to explosive eruptions (ex. felsic)

Question 21

what are some consequences of tephra?

Answer 21

• hazard to planes (can’t see)
• respiratory illness
• mass loading (too much weight from debris, rock is heavy)
• short-term climate effects
• tiny bits of glass ejected and lithic fragments

Question 22

what are pyroclastic flows?

Answer 22

fluid masses of rock fragments and gases that move rapidly in response to gravity (“flowing fire”

Question 23

what are some characteristics of pyroclastic flows?

Answer 23

• most common in explosive eruptions or lava dome collapses
• very fast, hot and dense ash flows

Question 24

what is a mudflow / lahar?

Answer 24

• debris flow composed of a slurry of pyroclastic material, rock debris and water

Question 25

what are some characteristics of mudflows?

Answer 25

• incredibly dangerous
• needs a water source (typically it is snow)
• far reaching
• concrete consistency
• hot!
• can get warm, melt glacier and snow, volcanic rock weak, can cause a flow

Question 26

what is a tsunami / landslide?

Answer 26

after volcano erupts or magma makes it to the surface and heats up the rock, displaced water and shock waves can cause a tsunami, and the heat can cause landslides

Question 27

what is an example of tsunami / landslide?

Answer 27

hunga tonga - hunga ha’apai

Question 28

what gasses make up volcanic emissions?

Answer 28

chlorine / hydrochloric acid
carbon dioxide
water vapor
fluoride / hydrofluoric acid
sulfur

Question 29

what are the three time scales that volcanoes can impact on the climate?

Answer 29

1. short-term cooling (large explosive eruptions)
2. long-term (effusive eruptions like flood basalts)
3. CO2 levels in the atmosphere (snowball earth)