volcanoes

Question 2

what’s the volcanic activity like on the plate boundaries

Answer 2

constructive = effusive (flowing) eruptions ( low VEI scale 1-3)
destructive = Explosive (moderate VIE 5-6)
collision = Usually none, fissure eruptions.
conservative = usually none, occasional fissure eruptions

VIE = volcanic explosivity index
fissure = narrow opening

Question 3

what was Hawaii created by and how are they formed

Answer 3

Hotspots- volcanic plumes which rise from the mantle through a crack in the plates creating land forms such as volcanoes

Question 4

what is Hawaii’s hot spot and volcanic eruptions

Answer 4

Hawaii is a midplate hot spot
some volcanoes eruptions are described as intra-plate ( distant from the boundaries )

Question 5

what are the primary and secondary hazards of volcanoes

Answer 5

Primary
- Lava flows
- pyroclastic flow
- tephra and ash falls
- gas eruptions

Secondary
- lahars
- Jokulhlaup ( Glacial Outbursts )

Question 6

What are lava flows and pyroclastic flows and what are the case studies linking to them

Answer 6

Lava flows - streams of lava that are very hot (1170) and can take years to cool . They usually aren’t dangerous due to low speeds but they destroy everything in their path.
case study = Hawaii 2018. May - August large lava flows covered the land and over 700 homes destroyed in the Puna district. Moved at speeds of 17mph

pyroclastic flows - mixture of hot rock, lava and ash. It moves rapidly and destroys everything they touch. Far more dangerous than lava flows. Very hot ( 700 ) and moves at around 100 km/h
case study = Fuego Guatemala 2018. Reached speeds of up to 450 mph and traveled miles. Temps ranged from 200 - 700. Started fires and destroy everything (69 deaths)

Question 7

What are tephra and ash falls and what are the case study’s linking

Answer 7

Tephra - pieces of volcanic rock and ash released into the air during eruptions heavier pieces land closer to the volcano and smaller land further and can cause injury and death
Ash falls - very disruptive, ash covers everything causing low visibility and roofs can cave in from the weight and if in car and plane engines it can clog them up

case study - Iceland 2010
Ash cloud reached up to 30,000 feet and disrupted flight paths and evacuations had to occur to stop people breathing in too much gas

Question 8

what are gas eruptions and what are the case studies

Answer 8

They are gases from magma which are released (magma plumes) and they can effect people, animals and structures and lead to global dimming and can travel for thousands of miles
case study = Mt Pinatubo 1991 it produced 20 million tonnes of sulphur dioxide and the cloud rose to 32km. And it cooled earth by 0.6 degrees Celsius for 3 years

Question 9

What are lahars and jokulhlaup (glacial outbursts) and what are the case studies linking to them

Answer 9

lahars - masses of rock, mud and water moving very quickly down a volcano due to the heat of the volcano melting ice and snow. They can be hundreds of meters wide and are very quick.
case study = Columbia 1985 the pyroclastic flows melted snow and ice and water reached depths of 50m killing 23,000 over 100 km
jokulhlaup (glacial outbursts) = the heat of a volcanic eruption melting glaciers causing heavy and sudden flooding and release large amounts of sediment that can damage land
case study = Iceland 2010
rapid melting of a 200m glacier cause flooding and damaged Iceland ring road making evacuation almost impossible

Question 10

What are the different types of volcano and what are there properties?

Answer 10

. Shield Volcano - low with gently slopping sides. Basaltic lava so eruptions are gentle but frequent. Wide due to basaltic lava.
. Composite volcano - Formed from layers of ash and acidic lava. Rhyolitic lava so explosive due to thick, viscous lava. Narrow due to lava not flowing down. Ash clouds occur before lava
. Hotspot volcano - Hawaii is a hot spot volcano. Magma rising from a mantle plume. Lava accumulates on the ocean floor and cools creating land. As hotspot moves the volcano becomes extinct.

Question 11

What are the 3 magma types

Answer 11

Basaltic ( basalt )
Andesitic ( Andesite )
Rhyolitic ( Rhyolite )

Question 12

What are the properties of the lava types

Answer 12

basaltic
- 45 - 52 % silica content
- 1200 - 1000 degrees
- low viscosity ( runny )
- easy gas escape
- eruption is calm but frequent
Andesitic
- 52-66 % silica content
- 1000-800 degrees
- medium viscosity
- medium gas escape
- variable reactions
Rhyolitic
- 68-77 % of silica content
- 800 - 650 degrees
- high viscosity ( sticky )
- Difficult gas escape
- Explosive eruption