volcanic hazards Flashcards
what is vulcanicity
refers to all volcanic activities related to magma being forced into the crust
what are volcanoes
are openings in the Earth’s crust through which lava, ash and gases erupt
what is the difference between magma and lava
Molten rock beneath the surface is referred to as magma,
but once it is ejected at the surface it is called lava
how man active volcanoes are there
1500
how many volcanic eruptions are associated with plate margins
95%
how many volcanic eruptions are associated with intraplate
5%
what plate margins are volcanoes found at
- constructive (ocean crust)
- constructive (continental crust)
- destructive
- intraplate over hot posts
how does magma differ between constructive and destructive plate margins
constructive = basaltic
destructive = acidic (andesitic and rhyolite)
how does lava differ between constructive and destructive plate margins
constructive = runny, less viscous and low silica
destructive = slow moving, viscous and high silica
how does the type of eruption differ between constructive and destructive plate margins
constructive = little violence, effusive, gases escape
destructive = potentially explosive
how does the frequency of volcanic eruptions differ between constructive and destructive plate margins
constructive = regular and may be continuous
destructive = from time to time, long dormant periods
what is the spatial distribution of volcanoes
most occur in linear belts along plate boundaries e.g pacific ring of fire
what is magnitude in relation to volcanoes
refers to its explosive power
what scale measures volcanoes
since 1982 magnitude has been measured by a logarithmic scale known as the volcanic exclusivity index
what is the scale of the vei
1-8
how can we accurately predict an eruption
- vulcanologists need to know a volcanos eruption history
- and be currently monitoring it
what are the warning signs volcanologist monitor
- local seismic activity using seismometers, tremors indicate rising magma
- ground deformation measured by tilts meters
- changes in concentration of gasses e.g carbon dioxide and sulphur dioxide
- rising temp of ground water
- physical changes around the crater
what is a primary impact
occur immediately afterwards and are a
direct result of the material ejected from the volcano
what are examples of primary impacts from a volcanic eruption
- lava and pyroclastic flows destroy roads and cause buildings to collapse
- ash fall out may contaminate crops and water supplies
- tephras may kill or injure people
what are secondary impacts
occur in the days or weeks that follow and are indirectly related to the eruption itself, can be social, economic or environmental
examples of secondary impacts from volcanic eruptions
- Lahars can kill or injure people and can cause additional damage to roads and bridges, making it difficult for emergency services to reach people in need
- People who have lost loved ones or their home or job in the eruption can experience psychological problems
- Environmental impacts could include fires caused by lava flows and pyroclastic flows or damage to vegetation and fresh water habitats by acid rain
what risk management can be taken to reduce impacts of volcanoes
prediction and protection including preparedness, mitigation and adaption
what does prediction involve
- accurate hazard mapping
- analysing seismic shockwave patterns
- sampling gas and lava emissions
what is an example where prediction of volcanoes worked
2000 Mexico eruption of Popocatepetl, volcano erupted 48 hours after local population evacuation
what does protection involve
reducing risk of damage by preparing
- warnings are issued
- instructions given on how to react before, during and after
- hazard mapping and land use planning to avoid development in at risk areas
- in at risk areas, alert systems, shelters and evacuation maps, emergency food and water supplies
how can we adapt to volcanic eruptions
design solutions such as
- windows facing the volcano
- shutters for windows to make them air tight
- triple roof support for extra strength to prevent collapse
- steep slope roof and smooth roof material so ash is less likely to accumulate
- concrete rather than timber frames for additional strength
what is a lava flow
Molten rock flowing over the surface. Basaltic (basic) lavas have higher temperatures and a low silica content (less than 52%), which means that they tend to flow some distance before solidifying (e.g. on the Hawaiian Islands). Acid lavas (either andesitic or rhyolitic) are more viscous; flow more slowly and often solidifies in the vent of the volcano, resulting in unpredictable and explosive eruptions
what is a pyroclastic flow
A mixture of hot rock, lava, ash and gases rising from a volcanic eruption that moves at a rapid speed (up to 200m/s) along the ground. The most dangerous are those that erupt sideways due to a blocked summit crater. Temperatures are between 350- 1000oC. Pyroclastic flows are more common in eruptions of acidic lava at subduction zones
what is a tephra
Solid rock fragments ejected during volcanic eruptions. The largest fragments can be over 1m in diameter and fall close to the volcano (potentially causing injury or death to people); the smallest fragments (ash less than 2mm) are carried by wind and travel great distances (vertically and laterally)
what is a Nuees ardente
Means ‘glowing cloud’ and is a dense, rapidly moving cloud of hot gases, ashes and lava fragments from a volcanic eruption. It is a type of pyroclastic flow that contains more dense material and so doesn’t travel as far
What is ash fallout
Ash can be ejected high into the atmosphere and, depending on prevailing winds, can cover a large area. Ash is highly abrasive and can cause breathing problems, disrupt machinery and clog filters. It can also obstruct sunlight, reducing visibility and temperatures
What are volcanic gases
These are dominated by steam – often superheated – but also include carbon monoxide, hydrogen sulphide, sulphur dioxide and chlorine. These gases are highly dangerous
what are mudflows/lahars
Lahars are destructive mudflows formed when ash and other volcanic material are mixed with water. They flow at speeds of up to 60km/h and are highly erosive
what is acid rain
Volcanoes emit sulphurous gases, which can result in acidic rainwater when combined with atmospheric moisture
example of a pyroclastic flow
AD 79 from Mount Vesuvius overwhelmed the Roman city of Pempeii
what is an example of a lava flow
during 2014-15 eruption of Fogo Volcano in Cape Verde engulfed 75% of buildings within three villages
what is an example of a tephra
2010 eruption of Eyjajallajokull led to the cancellation of 100,000 flights
what is an example of a nuees ardente
1902 French Caribbean island of Martinique swept down the slopes of Mount Pelee killing all but 29,000 residents
what is an example of ash fallout
2010 eruption of Eyjafjallajokull
example of volcanic gasses
1986 -
At least 1,200 people were killed and
300 hospitalized when an underwater
volcanic explosion unleashed deadly gases at
Lake Nios in a remote area of northern
Cameroon
example of a mudflow/lahar
November 13, 1985 small eruption produced enormous lahar that buried the town of Armero in Tolima causing an estimated 25,000 deaths - deadliest lahar in recorded history
what is an example of acid rain
Tonga 2022 - Since the initial eruption, the volcano has been releasing sulfur dioxide and nitrogen oxide — two gases that create acid rain when they interact with water and oxygen in the atmosphere
