Global Hazards

Question 1

Explosive Volcano Features:

Answer 1

Composite volcano (stratovolcano)
Made up of layers of ash and acid lava
Concave symmetrical pattern
Internal lava flows -> minor igneous features such as sills and dykes
Acid magma -> doesn’t flow as easily -> volcanoes filled with solid magma -> prevents magma rising freely (acts as a plug) -> enormous pressure eventually released
So explosive that the top of the volcano is blown off -> creates a caldera

Question 2

Effusive Eruptions at shield volcanoes, what happens?

Answer 2

Effusive eruptions found at constructive plate boundaries
Most effusive eruptions occur at ocean floor (cannot see them)
Iceland- > One of the most active volcanic regions in the world
Basaltic lava -> gentle sloping sides
Successive flows accumulate for long enough, huge volcanoes are formed 10s of km

Question 3

What is a Lava Plateau

Answer 3

Basaltic magma erupts from multiple fissures (vast areas covered by free flowing lava -> flood basalts)
Columbia Plateau (USA) 130 000 km2
First formed -> no relief changes, uniform slope -> millions of years create more varied relief due to erosion and weathering
No large scale events taken place over last 50 million years

Question 4

What is the Volcanic Explosivity Index judged on

Answer 4

Magnitude: the amount of material erupted
Intensity: the speed at which material is erupted

Question 5

What is the Richter Scale/Facts about it

Answer 5

Developed in 1935
Uses seismic waves to determine magnitude
The scale is logarithmic so each whole number increase in magnitude represents a ten fold increase in the amplitude of the seismic wave
Represents a 30 fold increase in the release of energy
However does not show damage caused

Question 6

What is the Mercalli Scale/Facts about it

Answer 6

Measures intensity and its impact
It relates to ground movement that can be felt and seen
Qualitative assessment based upon observation and description

Question 7

Oceanic Plate Features:

Answer 7

Young, no older than 200 million years. Density - 3.0 kg/m3.
Minerals = basaltic and Sima (silicone and magnesium).

Question 8

Continental Plate Features:

Answer 8

Ancient.  
40% of Earth’s surface
70% of the volume of the crust.  
Average Thickness = 35km.  
Density - 2.6 kg/m3.   
Minerals = Granitic and Sial (silicone and aluminium)

Question 9

What is the Moment Magnitude scale

Answer 9

Measures energy released by the earthquake
Measures magnitude based on its seismic movement
The amount of energy released is related to geological properties such as rock rigidity
Largely replaced richter scale but can’t replace Mercalli Scale