Please enable JavaScript.
Coggle requires JavaScript to display documents.
Volcanic hazards (Magnitude and frequency (Icelandic (Magma flowing gently…
Volcanic hazards
Magnitude and frequency
Classified by explosivity, Power of eruption, VEI
Icelandic
Magma flowing gently through fissure
Plinian/ Vesuvian
Violent, andesitic in nature, large amount of material ejected
Hawaiian
Magma flowing gently from central vent
Krakatoan
Exceptionally violent, remove much of original cone
Strombolian
More violent, Andesitic in nature
Pelean/ Volcanian
Andesitic, pyroclastic flows
0= Quiet and effusive
1-3= more violent and cause localised damage
4-5= moderately explosive, regional scale damage
more than 6= gigantic in scale, global impacts, modify climate
Frequency can be determined by looking at deposits associated with it
Effusive eruptions will happen more regularly than explosive ones
Hazards
Flooding
Secondary, eruption melts glaciers and ice caps, also known as Jokulhlaup, melting of ice creates flood
Lahars
Secondary, melted snow and ice as result of eruption combined with ash, forms mud flows, move down rivers at high speeds, decelerate as moves downslope, stratocone volcanoes, picks up anything in path
Landslides
Secondary, mass movement may occur on side of volcano and send material plummeting, common on cones, destroy everything in path, 1km3 to 100km3 in size
Tsunamis
Secondary, sea waves generated by violent eruptions, result from violent submarine explosions, caused by caldera collapse, tectonic movement, pyroclastic flow discharge into sea, displaces water when hits sea
Gasses
Primary, CO2, CO, Hydrogen sulphide, Sulphur dioxide, Chlorine, released as pressure decreases, large pressure= explosion, can cause acid rain/ suffocate people/ climate change
Acid rain
Secondary, gasses released combines with atmosphere moisture to create acid rain, causes vegetation damage, corrodes buildings, kills fish, emissions of sulphur and NO
Pyroclastic Flows
Primary, hot, gas charged, high velocity flows made of gas and tephra, flow down sides of volcano, up to 700km/h, follow valleys, destroys everything in path
Climate change
Secondary, ejection of huge amounts of debris into atmosphere can block out sunlight and reduce global temp, Gasses can also cause global warming
Tephra
Primary, solid material varying in size ejected into atmosphere, explosive eruptions, Bomb= >64mm, Lapilli= 2-64mm, Ash= <2mm, can bury/ suffocate people and buildings
Lava Flows
Primary, streams of molten rock, Basic, intermediate or acid, viscous or non viscous, most can be easily avoided, cannot be stopped or diverted, hot (1,000-2,000 degrees)
Management
Often focuses on Prediction, Prevention and Protection. Prevention is impossible although may be possible to modify some hazards. Iceland= water sprayed onto lava, Sicily= Diversion channels
Prevention
Diverting lava, spraying water, barriers, blasting
Mitigation
Hazard resistant design, reduce impacts, channel lava, evacuation
Adaptation
Land use planning, modifying the loss, Hazard resistant design, evacuations, education, aid, temp housing
Preparedness
Evacuation, prediction, modifying vulnerability, warnings, monitoring, hazards resistant design, community preparedness
Protection is easier as location is known, Strategies used to predict eruptions by monitoring changes around the volcano, also monitor seismic activity
Protection takes range of forms, Evacuation can take place, Risk Assessments can be conducted by governments, Alert levels used to publicise threat
Scientists tasked with establishing threat, former eruption deposits used, Can be used to inform land use planning so no buildings in high risk areas
Can be classified as short and long term, may be some overlap between the 2, Short term= hours- weeks, Long term= weeks- years, Takes place before, during and after hazards, Short term= warnings, evacuating, Long term= clean up, research
impacts
Impacts may vary in scale, with small eruptions affecting immediate area but more explosive eruptions having a global impact
Possible to judge impacts on Primary (associated wit specific hazard) and Secondary(follows on from and result of primary ones)
Classifying hazards
Social
Economic
Environmental
Political
Long term
Short term
Affect MEDC/ LEDC, Urban/ Rural, Upland/ Lowland, Inland/ Coastal different
Vulcanicity, types of magma and plate boundaries
Vulcanicity
Cracks in crust which molten rock or lava are ejected during eruptions. nature of magma determines how hazardous and how explosive an eruption may be
Magma
Basaltic
45-50% SiO, 1000 degrees +, Runny viscosity and low gas content, Shield volcanoes, runny lava, no ash, Oceanic hotspots and constructive margins, Dry partial melting of Mantle Peridotite, non hazardous
Andesitic
55-60% SiO, 800 degrees, sticky and intermediate gas content, Composite volcanoes, lava and ash, Destructive margins, Wet partial melting of Mantle Peridotite, very hazardous
Ryholitic
65% SiO, 700 degrees, very sticky and high gas content, pyroclastic flows, ash, Continental hotspots, collisional margins, Wet partial melting of Continental Crust very hazardous but rare
Classified according to SiO content, 3 types, differ according to viscosity
Type of magma determined by nature of crust
Constructive boundaries= Basaltic, Destructive OC-OC= Intermediate, Destructive OC-CO= Rhyolitic
More acidic= more explosive, if gasses escape it will be more effusive and less explosive
Type of volcano
Fissure
Katla, Iceland, Cracks or faults, non-explosive, basic magma
Shield
Broad gentle slope, fluid lava, flow eruption, not explosive, Hawaii
Caldera
Circular depression, sudden collapse of crater, Toba= 30 X 100km, Santorini, Mediterranean
Dome
Rapidly cooling viscous lava creates dome, explosive eruptions, Puys, France
Cinder cone
Mounds of Basaltic magma, Hekla, Iceland
Composite
Cone shaped, alternate layers of ash and lava, explosive eruptions, Vesuvius, Italy
Nature and distribution
Volcanoes located at Constructive margins, Destructive margins and Hotspots