4. Volcanoes Flashcards
What is a volcano?
• A volcano occurs when the molten magma forces its way up to the earth’s surface either through a vent (hole) or through a fissure (large cracks).
What is magma called when it reaches the surface?
Lava
What do vent eruptions lead to?
A vent eruption leads to the formation of a cone-shaped mountain.
What does a fissure eruption lead to?
Fissure eruptions lead to the formation of a wider and flatter
plateau.
How many active volcanoes above the ocean’s surface?
600
How many volcanoes erupt on average each year?
50
What is an active volcano?
Active: a volcano that continuously erupts, erupted recently or is likely to erupt in the near future, e.g. Mt Etna or Stromboli in Italy and Mauna Loa, Hawaii
What is a dormant volcano?
Dormant: a volcano that has not erupted for a very long time (+100 yrs.) but may do so again. The Yellowstone National Park volcano has been dormant for 640,000 years while Mount St Helens in the US was dormant for 123 years before its 1980 eruption. Mount Pinatubo in the Philippines had not erupted in 600 years before its 1995 eruption.
What is an extinct volcano?
Extinct: a volcano that has not erupted in recorded history, e.g. Slemish Co. Antrim has not erupted in 15 million years as Ireland moved away from a plate boundary.
What are the two types of lava?
Acidic and basic lava
What is acidic lava?
- very explosive/violent
- less hot (800c)
- Steep sided volcanoes
- Convergent, boundaries at subduction zones
- Doesn’t flow easily/viscous= trapped gases
What is basic lava?
- Non-explosive/ gentle eruptions
- Fluid and runny= few trapped gases
- extremely hot (1200c)
- Divergent plate boundaries and hotspots
- Forms shield volcanoes, lava plateaus
- Low silica content
What is pyroclastic flow?
Pyroclastic flows are boiling clouds of ash and rock which will travel at speeds of up to 600 km/hr. These flows are also called nuée ardentes.
What is pumice?
• Pumice is created when lava mixes with air, causing it to fill with air bubbles.
What are pyroclasts?
Pyroclasts are hot ash, lava and rock fragments thrown out by a volcano and are sometimes referred to as volcanic bombs.
What are examples of volcanic gases?
• Volcanic gases include: carbon monoxide, carbon dioxide, sulphur dioxide and chlorine.
Example of the effect of poisonous volcanic gases?
• In 1986 in Cameroon, carbon dioxide from Lake Nyos (a lake in the crater of an inactive volcano) leaked in to the atmosphere and killed 1700 people.
Where does water vapour release from a volcano and what effect does it have?
Volcanoes at subduction zones involving an oceanic plate release huge amounts of water vapour.
• As the water vapour rises it cools rapidly and causes torrential downpours. This intense rainfall mixed with lava, ash and rock fragments can lead to deadly lahars. The water content of lahars and their ability to flow is increased further when an eruption occurs on top of a snow-covered mountain peak.
What is tephra?
Pyroclastic material that is deposited by falling through the air, from a high ash cloud
E.g Cumbre Vieja, La Palma, Spain 2021
Negative effects of Volcanoes?
- Loss of Life e.g Mt Vesuvius 79 AD 10,000
- Lahars e.g Armero, Colombia 1985 23,000
- Poisonous Gases e.g Lake Nyos, Cameroon 1986 1700
- Disruption to Air Travel e.g Eyjafjnallajokull 2010 €140 per day
Positive Effects of Volcanic Activity?
- Geothermal Energy e.g groundwater superheated-wells drilled- 90% of homes heated by geothermal
- Tourism e.g Iceland 2.5 m tourists- €3b- Mt Etna, Hekla
- Fertile Soils e.g Ash and cinders rich in nutrients- Hawaii pineapple and sugar crops on volcanic soils
Predicting volcanic activity?
- Seismic Activity e.g as magma rises it causes the rocks to vibrate
- Ground Deformation e.g Mt St.Helens swelled 1.5 m per day before 1980 eruption, EDMs, Tiltmeters, GPS
- Gas emissions e.g Mt Pinatubo 500-5000 tonnes of sulphur dioxide
- History of volcanic eruptions e.g Mt Katla Iceland every 80 years, 1918
What are extrusive volcanic landforms?
- Volcanic comes
- Hotspots
- Fissures
What are examples of intrusive volcanic landforms?
- Batholiths
- Sills
- Dykes
- Lacoliths
- Lopoliths
What are cinder volcanoes?
- <300 m in height
- Steep sides
- Explosive eruptions at convergent boundaries
- Erupt once in their lifetime
What are composite volcanoes?
- Convergent boundaries during violent eruptions
- Acidic lava
- Alternate layers of lava and pyroclasts
- Steep sides
- e.g Mt Etna
What are dome volcanoes?
- viscous lava gets pushed out of the vent and hardens
- creates a lid on the volcano
- violent eruptions
- e.g Mt St Helen’s
What is a shield volcano?
- Form at hotspots (sometimes divergent boundaries)
- non violent eruptions
- basic lava
- layers of lava built up
- gently sloping sides
- e.g Mauna Loa, Hawaii- 120km base
What is a caldera?
When a magma changer is emptied, the volcanic material above the chamber collapses into the empty magma chamber, it appears as a large cauldron shape, e.g Yellowstone National Park
What are laccoliths?
Dome like structures of hard intrusive igneous rock that bulged upwards against the overlying rock strata
What are lopoliths?
Dome like structure of hard intrusive igneous rock that sags downwards
What are sills?
Horizontal sheets of igneous rock that run parallel to the under and overlying rock strata. They form when magma forces its way into the bedding planes of sedimentary rock where it cooled and solidified
What are dykes?
Vertical sheets of volcanic rock that cooled and solidified in vertical cracks in the crust
