Volcanic Eruptions Flashcards
Define Ash Cloud?
Can reach up to 14km into the stratosphere.
This includes anything ejected from the volcano - ash, dust, rock are all ejectied.
Define Lava flow?
Liquid/ solidified lava
Can flow from a volcanic vent down the side of a volcano
Speed and Distance of eruption depend on TEMPERATURE and VISCOICTY of the lava
Define Mud flow?
Also known as a LAHAR
A flowing mass of unconsolidated earth and fine grained debris
(volcanic material+ water= Lahar)
Define Pyroclastic and Ash Fallout?
Pyroclastic= an avalanche of got moving volcanic ash and gas
Fallout or “tephra” can be small ash particles or large volcanic bombs of semi-molten rock
What are the main Volcanic gases?
CO2 and sulphur dioxide- can be harmful or breathed in.
What makes acid rain?
eg: sulphur dioxide reacts with water to create weak sulfuric acid
What are the three levels of magma/ lava thickness?
Basaltic- Runny and thin
Andesitic-Middle
Rhyolitic- Thick
What is the magnitude of Volcanoes measured in?
The Volcanic Explosivity Index (0-8) based on the amount of material ejected and how high it’s ejected.
What are the main types of Eruption?
In Hawaii Some Very Vintage People Poo
In order of Strength
Icelandic Hawaiian Strombolian Vulcanian Pelean Plinian
What are the main points regarding the Icelandic eruption?
- Named largely because these types of eruption are common in Iceland
- Basaltic (runny) lava flow
- Eruption height LESS than 1KM
- Regular/ continuous eruptions
What are the main points regarding the Hawaiian eruption?
- Basaltic lava (runny) flows from central vent
- Often a very calm eruption with not a lot of gas
- Lava is referred to as “pahoehoe” = smooth and relatively runny
- CONSTRUCTIVE margin
What are the main points regarding the Strombolian eruption?
- Named after the Stromboli volcano
- Slightly thicker Basalt lava
- Around 1-2 on the Volcanic Explosivity Index
- Volcanic bombs, steam
- CONSTRUCTIVE margin
What are the main points regarding the Vulcanian eruption?
- More violent but less frequent eruption
- Tends to be mostly Andesitic lava= lava is thicker= gases can’t escape and pressure builds
- 5-10km in the air
- Lava bombs and a pyroclastic flow
What are the main points regarding the Pelean eruption?
- Named after the destructive eruption of Mount Pelée on the Caribbean island of Martinique in 1902
- A violent eruption follows by a pyroclastic flow
- Large amounts of lava, dust and ash
- Very dangerous and SPORADIC
- DESTRUCTIVE
What are the main points regarding the Plinian eruption?
- Rhyolitic lava flow= VERY THICK
- Violent eruptions of gas that go up to at least 17km
- Due to dissolved gases in the magma chamber accumulating and eventually exploding
What are the main causes of the distribution of volcanoes?
- ocean ridges and sea floor spreading
- intra plate volcanism
- ocean rifts
- continental rifts
What happens at destructive , submerging zones?
Oceanic rift volcanism (going under/ subducting)
Ocean ridges occur due to the ocean lithosphere being thinned and stretched due to tectonic processes
=FISSURE eruptions take place
What happens at constructive, continental volcanism?
The lithosphere thins and stretches allowing the mantle to rise and create large RIFT VALLEYS
Define hot spot?
(Intra- plate Volcanism)- LOCALISED pockets of molten lava that rises through plumes to penetrate the surface
=For example, the Hawaiian Islands
Define a SHEILD VOLCANO and the characteristics of a shield volcano?
CONSTRUCTIVE
A shield volcano has gentle slopes and a wide base due to the thin, flowing lava that comes out of it’s creator
1 main vent=lots of lava reaches the surface
Gentle eruption- NO TEPHRA
BASALITIC LAVA- shields are a Basic form of armour= thin, runny, low viscosity, can travel far before it cools
Define a COMPOSITE VOLCANO?
DESTRUCTIVE
A composite volcano has steep gradient sides and a narrow base due to slow moving, thick lava which cools and sets before it gets too far
VIOLENT ERUPTIONS- force volcanic bombs out of the vent
Viscous, andesitic lava moves more slowly and cools quicker
Define volcano?
An opening vent in the earths crust through which lava, tephra and gases erupt
FISSURES AND FRACTURES in the earths crust create areas of low pressure that allows some molten rock to ascend and become EXTRUSIVE
(if rises but just into the crust and not fully= INTRUSTIVE)
Compare Basaltic and Andesitic lava?
BASALITIC =shield volcanoes =1,200 degrees Celsius =Low Viscosity- runny =Low silica- thin =Gentle but frequent =CONTRUCTIVE
ANDESITIC =composite volcanoes =800 degrees Celsius =High Viscosity- thick =High Silica- thick =Explosive but uncommon DESTRUCTIVE
How do we measure volcanic eruptions?
The Volcanic Explosivity Index (VEI)
A scale measurement of the volume of material erupted within an eruption- each eruption is separate
Hawaiian and Icelandic= at the BOTTOM of the scale 1-2
Super Volcanic eg: Yellowstone= at the TOP of the scale 7-8
What are the 5 main steps/ points involved within the formation of a hotspot volcano? (EXAM STYLE ANSWER)
- Radioactive decay within the earth’s core generates very hot temperatures
- If the decay is concentrated, hotspots will form upon the earths crust
- These hotspots heat the lower mantle, creating a LOCALISED THERMAL CURRENT where magma plumes rise vertically
- These plumes occasionally rise within the centre of plates (away from boundaries) and burn through the asthenosphere and lithosphere to create volcanic activity on the surface (INTRUSIVE ——– EXTRUSIVE)
- As the “hotspot” remains STATIONARY, the plate moves over the hotspot= a chain of active and subsequently extinct volcanoes
What are some of the PRIMARY IMPACTS of volcanic eruptions?
- Pyroclastic Flow- 800 degrees Celsius, Gas and Tephra, 700km/ hour
- Lava Flow
- Volcanic Gases- CO2, SO2- sulphur dioxide, Cl2- chlorine= POISIONOUS
- Tephra- any solid material ejected from the volcanoes crater
What are some of the SECONDARY IMPACTS of volcanic eruptions?
- ACID RAIN- gases, especially SO2- sulphur dioxide, react with rain which can decrease plant growth, contaminate water supplies and decrease fish stocks
- LAHARS- volcanic mudflows, melted snow and ice combines with ash to create a very fast moving pile of mud
- TSUNAMIS- caused due to the slipping of plates= earthquake= epicentre
- FLOODING- upon glacial areas if lava reaches them then ice will melt
How can we manage volcanic eruptions?
PREDICTION- Groundwater Levels will decrease
Monitor gas content within the air
Ground will swell- TILTOMETRES
Study previous eruptions/ history of eruptions of a specific volcano
PROTECTION- PRIOR WARNING- develop good alert systems
RED= evacuate the area
DIVERT LAVA FLOWS- man made channels
CONTROLLED, planned eruptions on the side of a volcano to divert the lava flow
An example of how developed countries have large scale development plans?
eg: Auckland, New Zealand- largest city and on an active monogenetic volcanic field- large scale evacuation plan
(Population of 1.5 million)
Define the Benioff Zone?
The part of a subduction zone where dense, oceanic plate begins to melt to form magma.
Define the Benioff Zone?
The part of a subduction zone where dense, oceanic plate begins to melt to form magma.
