hazardous earth 1

Question 1

what is the asthenosphere and lithosphere and crust types?

Answer 1

lithosphere - The rigid layer comprising the crust and the upper mantle above the asthenosphere..
asthenosphere - The semi-molten or viscous layer that extends from about 100km down to 300km down. It is part of the mantle that is capable of flowing slowly.

Continental crust has a density of 2.7 g/cm3, under land, 35km thick, 2.8 billion years old.
Oceanic crust has a density of 2.9 g/cm3, 7km thick, seafloor, 220 million years old.

Question 2

viscous and non-viscous lava

Answer 2

Non-viscous: Basaltic magma has a low silica content (48% silica) . It is found at divergent plate
boundaries and is responsible for effusive
eruptions.

Viscous: Andesitic magma has a high silica content (62%silica) and rhyolitic (71%). It is found at convergent plate
boundaries and is responsible for explosive
eruptions

Question 3

volcanoes at divergent and convergent margins

Answer 3

Convergent:
- Shape - tall and steep sided
- Magma type - andesitic - style
– explosive - frequency – infrequent
- materials erupted – lava, rocks, ash (tephra)
e.g. composite volcanoes, calderas

Divergent:
- Shape - low with gently sloping sides
- Magma type - basaltic
- style – effusive
- frequency – frequent
- materials erupted – only lava and gas
e.g. shield volcanoes and fissure eruptions

Question 4

hotspots - cause and over time and supervolcanoes

Answer 4

A hotspot is a volcano that is not at a plate boundary. It is caused by excessive heat from the core-mantle boundary. The hot rock rises as a mantle plume because it is less dense than the surrounding rock in the asthenosphere.

Over time it becomes an extinct volcano as the plate moves away from the mantle plume. The hot spot volcano gets worn down by wave erosion and becomes a flat topped submarine volcano called a GUYOT.

super volcanoes: It erupts at least 1,000 km3 of material (a large volcano erupts around 1 km3) · it forms a giant caldera · often has a ridge of higher land around it · erupts infrequently

Question 5

hazards caused by volcanoes

Answer 5

1 lava flow
2 pyroclastic flows - fast moving clouds of hot gas and volcanic matter, travel 62-430 mph, reach 1000 degrees, move down slopes of volcanoes as they are denser than air
3 tephra - rock fragments and particles ejected by a volcanic eruption.
4 gas emissions
5 landslides
6 tsunami’s
7 Lahars - mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water
8 flooding
9 climate change

Question 6

how can volcanoes be mitigated and measured?

Answer 6

VEI: Uses a scale rating of 0 (least explosive) to 8 (most explosive), It combines magnitude and intensity.

1. seismicity - earthquakes are caused by the
   fracturing of rock as magma rises
2. Ground deformation - the ground can swell
   upwards suggesting that magma is moving
   up.
3. Gas emissions - there may be higher levels
   of sulphur dioxide and carbon dioxide
   before an eruption

Question 7

explain three ways volcanoes can be mititgated

Answer 7

1 lahar diversion channels EG Sakurajima in Japan
2. lava diversion EG mount Etna
3. Cooling lava to stop its flow EG Heimaey Iceland