Volcanicity Flashcards
What is volcanicity
Refers to all volcanic activities related to magma being forced into the crust which usually occurs at plate margins but not always.
Intrusive and Extrusive activity
Magma at high temperatures and high pressures exploits any weaknesses in the crust and erupts onto the surface as lava. Volcanic activity is either intrusive or extrusive depending on whether the magma breaks the surface or not
Classification of types of lava - Volcanic rock - Basalt
Silica content - 48-52%
Thin and runny
Eruption temperature - 1160 degrees C
Low viscosity, frequent but gentle, found at constructive plate margins and hot spots
Classification of types of lava - Volcanic rock - Andesite
Silica content - 52-63%
2nd hottest eruption temperature
high viscosity
ash rocks gases and lava ejected, pyroclastic flows likely
Found at destructive margins
Infrequent but violent eruptions
Classification of types of lava - Volcanic rock - Dacite
Silica content - 63-68%
Less hot
high viscosity
ash rocks gases and lava ejected, pyroclastic flows likely
Found at destructive margins
Infrequent but violent eruptions
Classification of types of lava - Volcanic rock - Rhyolite
Silica content - 68-77%
Thick and sticky
Eruption temperature - 900 degrees C
high viscosity
ash rocks gases and lava ejected, pyroclastic flows likely
Found at destructive margins
Infrequent but violent eruptions
Volcano Explosivity Index
Scale used to measure the relative explosiveness of volcanic eruptions.
Scale range - 0-8
Logarithmic - each step up represents a 10x increase in the volume of erupted material
Why do people live near volcanoes
Estimated that 500 million people live on or close to a volcano
- some places are well prepared so they feel safe
- people believe the chance of eruption is slim
- large amount of minerals
- tourism is popular
- cheap geothermal power
- poor cant afford to move away
Hazards to volcanicity
- flooding
- ash ruins crops
- dangerous lahars from volcanic melting of snow
- lava flows burn and bury crops
- pyroclastic flows destroy life and property
Benefits to volcanicity
- igneous rocks make excellent building materials
- lava flows can create new land
- lava and ashes weather quickly into fertile soil
- great tourist attractions
- volcanic dust absorbs solar energy and so lowers atmospheric temperatures
Type of volcanic eruption - Icelandic
Magma - Basaltic
Characteristics - effusive eruption with fissure vents, produces lava flows that spread over large areas
Type of volcanic eruption - Hawaiian
Magma - Basaltic
Characteristics - gentle eruptions, low gas content, fluid lava, shield volcanos
Type of volcanic eruption - Stromolian
Magma - basaltic to andesitic
Characteristics - moderate eruptions, distinct bursts of gas and lava, typically explosive but not very violent
Type of volcanic eruption - Vulcanian
Magma - Andesitic to rhyolitic
Characteristics - short violent and explosive, thick lava and high gas content, produces ash clouds and PF
Type of volcanic eruption - Vesuvian
Magma - Andesitic to Rhyolitic
Characteristics - large explosive eruptions ejecting ash high into atmosphere
Type of volcanic eruption - Pelean
Magma - Andesitic to Rhyolitic
Characteristics - extremely violent and produces destructive PF
Type of volcanic eruption - Plinian
Magma - Rhyolitic
Characteristics - catastrophic and explosive, towering columns of ash
Types of Volcano
1 - Fissure (Runnier Basaltic lava_
2 - Shield
3 - Dome
4 - Ash-cinder
5 - Composite/shield
6 - Caldera (Thinner Andesitic lava)
Instruments used to monitor volcanoes and what they are monitoring
Seismometers - seismic activity
Tiltometers - ground deformation
Magnetometers - upward movemnt of iron rich magma
Hydrological Instrumentation - rising groundwater temperature and or gas content
Remote sensing equipment - warning signs like small eruptions, emissions, landslides and rockfalls
Nuee Ardents (Pyroclastic Flows)
Fast moving, deadly mix of hot gas, ash and rock fragments
Tephra
Solid volcanic material of varying sizes ejected into the air, causing structural damage
Lahars
Mudflows formed by volcanic ash and water, destroying settlements and landscapes
