Volcanic Hazards Flashcards
Define pyroclastic flow
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
What is tephra
All fragments of rock ejected into the air by an erupting volcano.
Most tephra falls back onto the slopes of the volcano, enlarging it.
What is a lahar
Violent type of mudflow/debris flow composed of a slurry of pyroclastic material, rocky debris and water.
The material flows down from a volcano
Define nueé ardente
‘Glowing cloud’ - A dense, rapidly moving cloud of hot gases, ashes and lava fragments from a volcanic eruption (type of pyroclastic flow)
Define a caldera
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
Give an example of interplate eruptions
Hawaii
Give another name for a Strata Volcano
Composite Cone
Give 6 types of volcano
Fissure volcano
Shield Volcano
Dome Volcano
Ash Cinder Volcano
Composite Cone Volcano
Caldera
Describe a fissure volcano
Eruption along a crack in crust
Gentle basaltic slope of lava
Unexplosive magma - little impact to humans
(Iceland)
Describe a Shield Volcano
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)
Describe an acid dome volcano
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
Describe an ash cinder volcano
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.
Describe a composite cone volcano
Cone-shaped volcanoes built from many layers of vicious lava + ash cloud
Steep sides
Alternate layers of ash and lava
Pyroclastic flows + very explosive
Give an example of a stratovolcano
Mayan Volcano - Phillapenes
Give an example of a Caldera
Mount Bromo - Indonesia
How many active volcanoes are there in the world
1500
…% volcanos occur on the Pacific Ring of Fire
75%
What is the Volcanic Explosiivity Index
Measures the magnitude of volcanos
Give the 3 types of lava
Basaltic
Andesitic
Rhyolitic
Give the key characteristics of Basaltic lava
Silica content Temp Viscosity Volcanic products Eruption interval Location Processes
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
What is the hazard potential of basaltic lava
Not very hazardous as slow and unexplosive
Give the key characteristics of Adesetic lava
Silica content Temp Viscosity Volcanic products Eruption interval Location Processes
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
How hazardous is Adesetic lava
Very hazardous due to explosive eruptions
Give the key characteristics of Rhyolitic lava
Silica content Temp Viscosity Volcanic products Eruption interval Location Processes
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
How hazardous is Rhyolitic lava
Very hazardous due to extreme explosive eruptions (rare)
Give the 3 types of eruptions where basaltic lava is present
Icelandic
Hawaiian
Strombolian (thicker basaltic lava)
Give two eruptions that have andesitic lava
Vulcanian
Pelean (also has rhyolitic)
Give two eruptions that have rhyolitic lava
Pelean
Plinian
Rank the 6 different types of eruption in oder of explosively (lowest first)
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)
Give 5 patterns on the distribution of volcanoes around the world
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
How can one predict a volcanic event (5)
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
How can volcanic hazards be mitigated
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
Describe the causes and impacts of lava flows
- 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
Describe pyroclastic flows
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
Describe the causes and impacts of Nueé Adentes
Highly destructive , fast moving mass of gas
Consists of dense magma, fragments from a. lava dome
1902 - French Island Martinique killed 29,000
Describe the causes and impacts of Mud flow/lahars
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
Describe the causes and impacts of ash fallout
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
Describe the causes and impacts of gasses
During major eruption - large quantities of gas spewed out from mantle
Most common = CO2 and SO2
Health hazards = breathing difficulties. Crop damage
Give 3 ways pyroclastic flows are caused
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
