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A level Geography - Physical > Volcanic Hazards > Flashcards

Volcanic Hazards Flashcards

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1
Q

Define pyroclastic flow

A

A mixture of hot rock, lava, ash and gases arising from a. volcanic eruption that moves at rapid speed along the ground

300km/h + 2000C

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2
Q

What is tephra

A

All fragments of rock ejected into the air by an erupting volcano.
Most tephra falls back onto the slopes of the volcano, enlarging it.

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3
Q

What is a lahar

A

Violent type of mudflow/debris flow composed of a slurry of pyroclastic material, rocky debris and water.

The material flows down from a volcano

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4
Q

Define nueé ardente

A

‘Glowing cloud’ - A dense, rapidly moving cloud of hot gases, ashes and lava fragments from a volcanic eruption (type of pyroclastic flow)

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5
Q

Define a caldera

A

Large volcanic crater, often formed following. highly explosive eruption where the summit of the volcano is removed

Huge ash cloud - can block out sunlight causing volcanic winter - Impacting crop production + limiting biodiversity as some species won’t survive

Global tempters could drop by 2°C. However if large output of CO2, then global warming caused instead

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6
Q

Give an example of interplate eruptions

A

Hawaii

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7
Q

Give another name for a Strata Volcano

A

Composite Cone

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8
Q

Give 6 types of volcano

A

Fissure volcano

Shield Volcano

Dome Volcano

Ash Cinder Volcano

Composite Cone Volcano

Caldera

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9
Q

Describe a fissure volcano

A

Eruption along a crack in crust

Gentle basaltic slope of lava

Unexplosive magma - little impact to humans

(Iceland)

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10
Q

Describe a Shield Volcano

A

Gentle slope of basaltic lava flow - the lava flows for long distances before it solidifies

Constructieve plate margins

Less violent eruptions, creation of new land, enhances soil fertility in long run (2 years+)

(Mauna Loa - Hawaii)

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11
Q

Describe an acid dome volcano

A

Steep convex slope formed via the slow eruption of viscous lava from a volcano

Commonly encountered in the craters or on the flanks of large stratovolcanoes

Lots of SO2 gas producing acid rain . High levels fo gas impacting human health

Gas can impact water system - polluting drinking water

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12
Q

Describe an ash cinder volcano

A

Most common type

Form from explosions of hot magma cinders and ash . These cinders and ash settle around the main vent and build a steep sided cone. Very little lava is erupted from a cinder cone.

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13
Q

Describe a composite cone volcano

A

Cone-shaped volcanoes built from many layers of vicious lava + ash cloud

Steep sides

Alternate layers of ash and lava

Pyroclastic flows + very explosive

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14
Q

Give an example of a stratovolcano

A

Mayan Volcano - Phillapenes

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15
Q

Give an example of a Caldera

A

Mount Bromo - Indonesia

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16
Q

How many active volcanoes are there in the world

A

1500

17
Q

…% volcanos occur on the Pacific Ring of Fire

A

75%

18
Q

What is the Volcanic Explosiivity Index

A

Measures the magnitude of volcanos

19
Q

Give the 3 types of lava

A

Basaltic

Andesitic

Rhyolitic

20
Q

Give the key characteristics of Basaltic lava

Silica content
Temp
Viscosity 
Volcanic products 
Eruption interval 
Location 
Processes
A

Silica content = 50%

Temp = 1000C

Viscosity - Very runny, low gas

Volcanic products - Very hot runny lava

Eruption interval - Can be continuous (Hawaii)

Location - Oceanic hotspots + constructive plate margin

Processes - Dry partial melting of upper mantle/lower lithosphere, uncontaminated by sea water

21
Q

What is the hazard potential of basaltic lava

A

Not very hazardous as slow and unexplosive

22
Q

Give the key characteristics of Adesetic lava

Silica content
Temp
Viscosity 
Volcanic products 
Eruption interval 
Location 
Processes
A

Silica content = 60%

Temp = 800C

Viscosity - sticky, intermediate levels of gas

Volcanic products - Sticky lava flow, tephra, ash, gas, composite cone

Eruption interval - Decades/centuries

Location - Destructieve plate margin (subductive)

Processes - Wet partial melting of subducting oceanic crust contaminated by sea water and other materials;s

23
Q

How hazardous is Adesetic lava

A

Very hazardous due to explosive eruptions

24
Q

Give the key characteristics of Rhyolitic lava

Silica content
Temp
Viscosity 
Volcanic products 
Eruption interval 
Location 
Processes
A

Silica content = 65%

Temp = 700C

Viscosity - Very vicious , high gas

Volcanic products - Pyroclastic flows, ash, domes, gas

Eruption interval - Millennia

Location - Continental hotspots and continental - continental plate margins

Processes - In situ, melting of lower continental crust - magma mostly cools before reaching the surface

25
Q

How hazardous is Rhyolitic lava

A

Very hazardous due to extreme explosive eruptions (rare)

26
Q

Give the 3 types of eruptions where basaltic lava is present

A

Icelandic

Hawaiian

Strombolian (thicker basaltic lava)

27
Q

Give two eruptions that have andesitic lava

A

Vulcanian

Pelean (also has rhyolitic)

28
Q

Give two eruptions that have rhyolitic lava

A

Pelean

Plinian

29
Q

Rank the 6 different types of eruption in oder of explosively (lowest first)

A

Icelandic (fissures)

Hawaiin (gently flowing lava)

Strombolian (Frequent explosive eruptions of tephra but occasional short lava flows)

Vulcanian (less frequent but more violent

Pelean ( Very violent eruptions - pyroclastic flow)

Pilian (Exceptionally violent)

30
Q

Give 5 patterns on the distribution of volcanoes around the world

A

Large majority on destructive and constructive plate boundaries

Largely clustered on the Pacific Ring of Fire

Some anomalies locate don the middle of plates (Hawaii)

Cluster on Iceland

Centeral America = cluster

31
Q

How can one predict a volcanic event (5)

A

Analyse the history of eruptions in an area to gather patterns and the frequency

Rising groundwater temperature/gas content using hydrological instrumentation - Rising magma will heat groundwater and corrupt it with gases (Sulphur)

Ground deformation is measured using tiltometers and GPS. Indicates rising magma

Upwards movement or iron rich magma measured using magnetometers - Changing magnetism within the volcano is a common indication of rising magma

Siesmic activity meaured and recorded using. seismograph - micro quakes indicate rising magma and fracking/cracking of overlying rocks

32
Q

How can volcanic hazards be mitigated

A

Plan evacuation for people in nearby area

Stockpile food/water resources

Text alert whole population - allowing people to take appropriate action

Divert basaltic lava flow from infrastructure/people

33
Q

Describe the causes and impacts of lava flows

A
  • When magma erupts from a volcano
  • Severe burns, destroying of houses/agriculture/vegetation
  • Lava flows during the 2014 Fogo eruption in Cape Verda engulfed 75% buildings and 25% agriculture
34
Q

Describe pyroclastic flows

A

Made up of a high density mix of hot lava blocks, rock and gasses which move beneath an ash cloud.

Destroys everything in its path. 1000C+ and travels at 100-200mph

Mostly moves downhill but can move uphill if less dens e

Can move over water - pyroclastic surge

Consists of two parts - lower basal flow of cars fragments that move along ground, and a turbulent cloud of ash that rises above the basal flow

35
Q

Describe the causes and impacts of Nueé Adentes

A

Highly destructive , fast moving mass of gas

Consists of dense magma, fragments from a. lava dome

1902 - French Island Martinique killed 29,000

36
Q

Describe the causes and impacts of Mud flow/lahars

A

Destructive mud flow on slopes of volcano

20-40mph

Consists of mud, rock and water

Destroys infrastructure, severe flooding that follows can be long lasting

37
Q

Describe the causes and impacts of ash fallout

A

Formed during explosive eruptions when dissolved gases in magma expand and escape violently

Force of the gasses shatters the magma and propels it into the atmosphere where it solidifies into fragments of volcanic rock and glass.

Heavy ash fall kills crops and livestock. Breathing difficulties

Eyjallafolukull - glacial meltwater combined with meltwater to produce ash

38
Q

Describe the causes and impacts of gasses

A

During major eruption - large quantities of gas spewed out from mantle

Most common = CO2 and SO2

Health hazards = breathing difficulties. Crop damage

39
Q

Give 3 ways pyroclastic flows are caused

A

Boiling over from an eruptive vent
- During an explosive eruption, material is erupted without forming a high plume and rapidly moves downslope

Eruption column collapses
- During highly explosive eruptions, the column is ejected upwards into atmosphere + cools and becomes to dense to maintain upwards projection

Collapse of lava domes/flow
- Lava flow/domes van become so steep that they collapse due to gravitational force

A level Geography - Physical (19 decks)

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