Volcanoes

Question 0

What makes a volcano explosive?

Answer 0

High silica –> viscous –> has is trapped –> pressure builds up

Question 1

Define volcano

Answer 1

A vent at the earths surface through which magma and other volcanic materials are ejected

Question 2

Some gases released by volcanoes?

Answer 2

Water vapour, CO2, SO2, N2,

Bit of H, Cl, F, CO, Ar, S

Question 3

Impacts of volcanic gases

Answer 3

Asphyxiation, acid rain, global decrease in temperature

Question 4

Define viscosity of a magma

Answer 4

Measure of a resistance to flow. Determined by silica content

Question 5

What do magic lavas cool to form?

Answer 5

Aa lava flows (rough, blocky and jagged surface)
Pahoehoe flows (ropey and smooth)

Question 6

Define pyroclastic rocks

Answer 6

Forms when pyroclastic material is compacted into a solid rock

Question 7

Describe ash

Answer 7

The smallest particles smaller than 2mm and forms the pyroclastic rock “tuff” when consolidated

Question 8

Describe lapilli

Answer 8

Particles between 2-64mm and form a “lapilli tuff”

Question 9

Describe volcanic bombs

Answer 9

Coarsest particles (>64). 
Form the pyro clastic rock agglomerate and form nearest to the crater of the volcano

Question 10

Define pyroclastic flows

Answer 10

Super-heated, fast-flowing, turbulent cloud of gas and ash

Question 11

What do pyroclastic flows cool to form?

Answer 11

The rock ignimbrite

Contains pieces of pumice known as fiame

Question 12

What are lahars?

Answer 12

Unconsolidated ash, rock, and pyroclastic deposits which become saturated from water from lakes and rivers or melted snow or ice to produce a fast flowing cement like mudflow

Question 13

What is an isopachyte?

Answer 13

A map where there is a line joining points of equal thickness of deposit. Resultant map is called an isopach map.

Question 14

What will effect the distribution of volcanic products?

Answer 14

Grain size,
Wind,
Energy / type of blast
Viscosity of lavas
Topography determining lahar distribution

Question 15

Are mafic eruptions frequent or not?

Answer 15

Yes they are frequent

Question 16

Do mafic magmas have a high or low viscosity?

Answer 16

Low viscosity

Question 17

What type of volcanoes do mafic eruptions create?

Answer 17

Shield volcanoes

Question 18

Which type of eruptions are effusive?

Answer 18

Mafic eruptions

Question 19

What does effusive mean?

Answer 19

Used to describe the fluid, non explosive nature of basaltic lava

Question 20

Which types of plate boundaries do mafic eruptions take place at?

Answer 20

Divergent and hot spots

Question 21

Shield volcano example?

Answer 21

Mauna Loa in Hawaii (from the sea floor is 150km wide at the base)

Question 22

What is the gradient of the slope of shield volcanoes?

Answer 22

10 degrees

Question 23

Why are the flanks of volcanoes slightly steeper?

Answer 23

As the magma travels it cools and the viscosity increases

Question 24

What are fissure eruptions?

Answer 24

Where the magma reaches the surface along long linear cracks or fissures. They are basaltic and effusive eruptions

Question 25

Which type of boundaries do explosive volcanoes accurate at?

Answer 25

Convergent | Particularly around the Pacific Ocean - ring of fire

Question 26

Do explosive eruptions have high or low viscosity magma?

Answer 26

High viscosity

Question 27

Two examples of thick magmas?

Answer 27

Andesite and rhyolite

Question 28

Gradient of slope of composite / strato volcanoes?

Answer 28

Over 30 degrees

Question 29

Size of explosive volcanoes on the VEI scale?

Answer 29

2 - 8

Question 30

What percent of the material ejected is pyroclastic in explosive eruptions?

Answer 30

50%

Question 31

Eruption style of explosive volcanoes can be described as?

Answer 31

Strombolian, volcanian, Orleans, Plinian

Question 32

What percentage of volcanoes are composite volcanoes?

Answer 32

60%

Question 33

What's a dormant volcano?

Answer 33

When there is a period of no activity (magma chamber filling with magma)

Question 34

When will there be a volcano?

Answer 34

Pressure inside the volcano exceeds the weight of the overlying rock creating an explosion

Question 35

How do calderas form?

Answer 35

Magma chamber empties due to a series of explosive eruptions Volcano begins to collapse into weakened area. The compression makes more violent eruptions. Entire volcano collapses. Can cause tsunamis if on island or coast

Question 36

What does superheated mean?

Answer 36

Very hot but pressure prevents liquids from turning into gasses

Question 37

Define geyser

Answer 37

Hot springs from which a column of superheated water is explosively discharged at regular intervals

Question 38

Define an active volcano

Answer 38

Shows eruptive activity within recorded history.

Question 39

Define an extinct volcano

Answer 39

Not shown any historic activity and is usually deeply eroded

Question 40

Active volcano example?

Answer 40

My St. Helens

Question 41

Dormant volcano example?

Answer 41

Yellowstone

Question 42

Extinct volcano example?

Answer 42

Borrowdale

Question 43

Methods of predicting earthquakes?

Answer 43

Historic patterns of activity - how frequent and composition

Question 44

What does studying the distribution of volcanic material tell us about the volcano?

Answer 44

The type of eruption eg lateral blast Strength or magnitude. Volume of it gives explosivity

Question 45

Swelling of the ground can indicate a volcano will erupt. What is it measured with?

Answer 45

Tiltmetres and GPS

Question 46

How can gas emissions indicate a volcano will erupt?

Answer 46

As magma bears the surface it's pressure decreases and pressure escapes. Increasing amounts of gasses eg SO2 being released suggest that magma is nearing the surface

Question 47

Earthquakes commonly provide the earliest warning of eruptions. Which are the 3 types of earthquakes?

Answer 47

Short period Long period Harmonic tremors

Question 48

What are short period earthquakes caused by?

Answer 48

Fracturing of brittle rock as magma forces it's way upwards

Question 49

What are long period earthquakes caused by?

Answer 49

Increasing gas pressure in the magma chamber

Question 50

What are harmonic tremor earthquakes caused by?

Answer 50

Magma vibrating in the feeder pipe as it moves upwards

Question 51

What is Nuée ardentes?

Answer 51

Gaseous magma that forms the fast moving pyroclastic flows and cools to form the rock ignimbrite