Lecture #8 -Volcanoes Flashcards Preview

Geo of Hazards > Lecture #8 -Volcanoes > Flashcards

Flashcards in Lecture #8 -Volcanoes Deck (46):
1

Where are most volcanoes occur?

Located near plate boundaries

2

What is Magma?

liquid rock found deep within the crust and upper mantle

3

What is Lava?

Liquid rock found drown for and erupting volcano (basically magma the reaches earths surface)

4

What are the most abundant elements in magma?

Silica and Oxygen
-together they form silica

5

What is the order of rocks from lowest to highest

Basalt
Andesite
Dacite
Rhyolite

6

What does a higher silica content produce?

a bigger explosion

7

What determines the shapes of volcanoes?

Chemistry and viscosity of magma

8

What are characteristics of magma with a high silica content?

Cooler
More viscous
More gases
explosive eruption

9

What are characteristics of magma with a low silica content?

Hotter
less viscous
Fewer gases
not as explosive

10

What are the 4 types of Volcanoes?

1. Shield
2. Composite
3. Volcanic Domes
4.Cinder Cones

11

Characteristics of Sheild Volcanoes

Form from lava(erupts, cools hardens)
basaltic magma
Not really explosive

12

What is Tephra?

A general term for fragmented material ejected during an explosion

13

Characteristic of Shield Volcanoes?

Form from lava flow and pyroclastic deposits
Andesitic or Dacitic
Eruptions more explosive but less frequent

14

Characteristics of Volcanic Domes?

Highly viscous rhyolitic magma
Steep sided mounts that form around vents

15

Characteristics of Cinder Cone volcanoes

smaller volcanoes made from small pieces of tephra
Round--> oval Shape
Contain a crater at the top of the volcanoe

16

What is a Maars?

Circular volcanic craters produced by an explosive eruption and fill with water

17

What Causes Maars?

When groundwater comes into contact with magma which creates an explosion

18

What are Ice Volcanoes?

When volcanoes erupt beneath or against glaciers

19

What do Ice volcanoes produce?

jökuhloups
-when magma melts large quantities of ice and produce floods

20

What is a crater?

Depression formed by the explosion or collapse of a volcano top.
-up to 2km in diamerter

21

What is a volcanic vent?

An opening on the surface through which lava and pyroclastic debris erupt.

22

Does lava always erupt out of the top?

No, can erupt from fissures in the side

23

what is a Caldera

Circular to oval depression formed during the collapse of a volcano.
-Up to 25km in diameter

24

How do calderas form?

The collapse of a magma chamber below a composite volcano during an explosive eruption. The chamber become empty and pressures decreases so it doesn't have the support and therefore collapses

25

What is a hot spring?

Heated groundwater that discharges at the surface

26

What is a geyser?

ground water that boils in an underground chamber and periodically produce a release of steam or water

27

When does Old faithful erupt?

Found in Yellowstone National Park
Erupts for 2-3 mins
every 70 mins
50m high

28

what are Super eruptions

Are the products of super volcanoes and are hella rare
-occur when a high volume of magma rises and is unable to break though the crust until enough pressure builds up

29

Subduction Zone volcanoe characteristics

Andesite
Composite volcanoes found here

30

Mid ocean ridge volcano characteristics

Basaltic
Shield volcanoes

31

Characteristics of volcanoes at hot spots beneath the ocean

Basaltic
Chains of Shield Volcanoes
-Islands

32

Characteristics of volcanoes at hotspots beneath continental crust

Rhyolitic
Explosive eruptions
Commonly forms Claderas
Ex: Yellowstone

33

Why arent death tolls higher for volcanoes?

They occur in high mountain ranges and not a lot of people live there

34

What are some primary effects of volcanoes

Lava flows
pyroclastic flow
Ash falls
lateral blasts

35

What are some secondary effects of volcanoes?

Landslides
Floods
Fires
Tsunamis
Lahars

36

What is Pahoehoe lava?

low viscosity
Really hot
When hardened has a smooth texture

37

What is AA lava?

High viscosity
lower temperatures
When hardened has a blocky texture

38

What is a Pyroclastic Flow?

Avalanches of ash, gas and rock fragments that travel down the slope of a volcano during an explosive eruption
- more people have actually died form these than an actual explosion

39

What is an Ash fall?

particles of ash can be carried downwind hindered of km form the eruption site

40

What is a Sector Collapse?

Flank of volcanoes can collapse at any time
-as magma travels up the channel, it can inflate and its slopes can be oversteepened

41

What is a Lahar?

Large amount of material that become saturated with water and moves downslope

42

Characteristics of Mt St Helen?

March 1980
-small explosions were evident due to ground water contacting magma
-Bulge began to grown on the flank of the mountain
-M 5.1 quake caused the bulge to break off
-Lateral blast occurred
-57 people died mainly because of pyroclastic flows
-left behind a barren landscape

43

What other hazards can volcanoes cause?

-Lava can catch things on fire
-Earthquakes
-Landslide
-Jökulhaups

44

What are natural service functions of volcanoes?

Provided gases that sustain the atmosphere
Geothermal energy and heat
Attract tourism and recreation
Creates new land

45

How do we minimize Volcanic hazards?

1. Monitoring seismic activity
2. Thermal and hydraulic monitoring
3. Land Surface monitoring
4. Monitoring volcanic gas emissions
5. understanding local and geologic history

46

What are the 3 methods in attempting to divert lava flows?

1. Bombing- forcing channel to an alternate rout
2. Hydraulic Chilling- water used to chill and cool lava
3. wall Construction- Wall redirecting