Volcanic hazards
Encyclopedia
Volcanic hazards are threats to life and/or infrastructure due to volcanic
activity and related phenomena such as floods and landslides at volcanoes.
lava that can provide different hazard
s. Pahoehoe lava is smooth and ropy while Aa lava is blocky and hard. Lava flows normally follow the topography, sinking into depressions and valley
s and flowing down the volcano. Lava flows will bury roads farmland
s and other forms of personal property. This lava could destroy homes, cars, and lives standing in the way. Lava flows are dangerous, however, they are slow moving and this gives people time to respond and evacuate out of immediate areas. People can mitigate this hazard by not moving to valley or depressed areas around a volcano.
is a generalized word for the various bits of debris that are launched out of a volcano during an eruption, regardless of their size. Pyroclastic materials are generally categorized according to size: dust measures at <1/8 mm, ash is 1/8–2 mm, cinders are 2–64 mm, and bombs
and blocks are both >64 mm. There are different hazards associated with the different kinds of pyroclastic materials. Dust and ash could coat cars and homes, rendering the car unable to drive with dust accumulation in the engine. They could also layer on homes and add weight to roofs causing the house to collapse. Also, ash and dust inhaled could cause long-term respiratory
issues in people inhaling the particles. Cinders are flaming pieces of ejected volcanic material which could set fire to homes and wooded areas. Bombs and blocks run the risk of hitting various objects and people within range of the volcano. Projectiles can be thrown thousands of feet in the air and can be found several miles away from the initial eruption point.
A pyroclastic flow
is a fast-moving (up to 700 km/hr) extremely hot (~1000°C) mass of air and tephra that charges down the sides of a volcano during an explosive eruption
.
or river
, they can turn the watercourse into a fast moving mudflow
s. These are called lahar
s; when the lahar contains large material such as blocks of rock and trees, it is a volcanic debris flow
. Lahars can form directly from a pyroclastic material flow flowing into a river, or could possiblly form after the main eruption. The latter is referred to as secondary lahars and form when rain wets the ash and debris already on a landscape and stick together rolling along the topography. It's estimated that it can only take 30% water to initiate ash into a lahar. The thicker and/or more fast-moving a lahar, the more potential to destroy things in its path, thus making it more dangerous than a slower and/or more diluted lahar. Lahars and mudflows can damage buildings, wildlife
and cars and can prove difficult to escape once caught in them. The lahars can coat objects, wash objects away and can knock objects down by their force. Lahars, debris flows and mudflows that travel into a river or stream run the potential for crowding the waterway, forcing the water to flow outward and causing a flood. The volcanic matter could also pollute the water, making it unsafe to drink.
The debris that is ejected from the volcano adds to the sides of the slope with each eruption, making the sides steeper each time. Eventually the slope gets so steep that it fails and an avalanche ensues. These avalanches carry material and debris for very long distances at very short intervals. This makes a warning system nearly immposible because the slope failure could occur at any time. The avalanche will destroy anything in its path including personal property, houses, buildings, vehicles and possibly even wildlife. If the impact of the materials in the avalanche doesn't destroy the person or object at first contact, there could be damage resulting from the weight of prolonged material on the objects.
s can occur due to volcanic activity. These earthquakes could produce topographical deformation and/or destruction of buildings, homes, cars, etc. There are two different types of these earthquakes: volcano-tectonic earthquakes and long period earthquakes. "Earthquakes produced by stress changes in solid rock due to the injection or withdrawal of magma (molton rock) are called volcano-tectonic earthquakes". These are hazardous due to the possibility of ground cracks or slope failures, therefore destroying everything in its path. Long Period earthquakes, which happen when magma is suddenly forced into the surrounding rocks, are generally seen as a precursor to the actual eruption.
The United States Geological Survey is now currently monitoring volcanic activity all around the world. By monitoring the seismic and geological activity, the USGS can warn people ahead of time about impending danger. These volcanologists measure the size of an eruption in two ways: the eruption magnitude (by the volume or mass of magma erupted) and eruption intensity (by the rate of magma erupted). There are also various forms of satellites and imagery, such as satellite InSAR imagery, that monnitor the activity that isn't exposed to the naked eye.
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
activity and related phenomena such as floods and landslides at volcanoes.
Lava flows
There are different forms of effusiveEffusive eruption
An effusive eruption is a volcanic eruption characterized by the outpouring of lava onto the ground...
lava that can provide different hazard
Hazard
A hazard is a situation that poses a level of threat to life, health, property, or environment. Most hazards are dormant or potential, with only a theoretical risk of harm; however, once a hazard becomes "active", it can create an emergency situation. A hazard does not exist when it is not...
s. Pahoehoe lava is smooth and ropy while Aa lava is blocky and hard. Lava flows normally follow the topography, sinking into depressions and valley
Valley
In geology, a valley or dale is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys...
s and flowing down the volcano. Lava flows will bury roads farmland
Farmland
Farmland generally refers to agricultural land, or land currently used for the purposes of farming. It may also refer to:*Arable land, land capable of cultivating crops*Farmland, Indiana, a town in the United States...
s and other forms of personal property. This lava could destroy homes, cars, and lives standing in the way. Lava flows are dangerous, however, they are slow moving and this gives people time to respond and evacuate out of immediate areas. People can mitigate this hazard by not moving to valley or depressed areas around a volcano.
Pyroclastic materials (tephra) and flow
TephraTephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
is a generalized word for the various bits of debris that are launched out of a volcano during an eruption, regardless of their size. Pyroclastic materials are generally categorized according to size: dust measures at <1/8 mm, ash is 1/8–2 mm, cinders are 2–64 mm, and bombs
Volcanic bomb
A volcanic bomb is a mass of molten rock larger than 65 mm in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they do not have grains...
and blocks are both >64 mm. There are different hazards associated with the different kinds of pyroclastic materials. Dust and ash could coat cars and homes, rendering the car unable to drive with dust accumulation in the engine. They could also layer on homes and add weight to roofs causing the house to collapse. Also, ash and dust inhaled could cause long-term respiratory
Respiratory system
The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...
issues in people inhaling the particles. Cinders are flaming pieces of ejected volcanic material which could set fire to homes and wooded areas. Bombs and blocks run the risk of hitting various objects and people within range of the volcano. Projectiles can be thrown thousands of feet in the air and can be found several miles away from the initial eruption point.
A pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
is a fast-moving (up to 700 km/hr) extremely hot (~1000°C) mass of air and tephra that charges down the sides of a volcano during an explosive eruption
Explosive eruption
An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example. Such an eruption is driven by gas accumulating under great pressure. Driven by hot rising magma, it interacts with ground water until the pressure increases to the...
.
Mudflows, floods, debris flows and avalanches
When pyroclastic materials mix with water from a nearby streamStream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
or river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
, they can turn the watercourse into a fast moving mudflow
Mudflow
A mudslide is the most rapid and fluid type of downhill mass wasting. It is a rapid movement of a large mass of mud formed from loose soil and water. Similar terms are mudflow, mud stream, debris flow A mudslide is the most rapid (up to 80 km/h, or 50 mph) and fluid type of downhill mass...
s. These are called lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
s; when the lahar contains large material such as blocks of rock and trees, it is a volcanic debris flow
Debris flow
A debris flow is a fast moving, liquefied landslide of unconsolidated, saturated debris that looks like flowing concrete. It is differentiated from a mudflow in terms of the viscosity and textural properties of the flow. Flows can carry material ranging in size from clay to boulders, and may...
. Lahars can form directly from a pyroclastic material flow flowing into a river, or could possiblly form after the main eruption. The latter is referred to as secondary lahars and form when rain wets the ash and debris already on a landscape and stick together rolling along the topography. It's estimated that it can only take 30% water to initiate ash into a lahar. The thicker and/or more fast-moving a lahar, the more potential to destroy things in its path, thus making it more dangerous than a slower and/or more diluted lahar. Lahars and mudflows can damage buildings, wildlife
Wildlife
Wildlife includes all non-domesticated plants, animals and other organisms. Domesticating wild plant and animal species for human benefit has occurred many times all over the planet, and has a major impact on the environment, both positive and negative....
and cars and can prove difficult to escape once caught in them. The lahars can coat objects, wash objects away and can knock objects down by their force. Lahars, debris flows and mudflows that travel into a river or stream run the potential for crowding the waterway, forcing the water to flow outward and causing a flood. The volcanic matter could also pollute the water, making it unsafe to drink.
The debris that is ejected from the volcano adds to the sides of the slope with each eruption, making the sides steeper each time. Eventually the slope gets so steep that it fails and an avalanche ensues. These avalanches carry material and debris for very long distances at very short intervals. This makes a warning system nearly immposible because the slope failure could occur at any time. The avalanche will destroy anything in its path including personal property, houses, buildings, vehicles and possibly even wildlife. If the impact of the materials in the avalanche doesn't destroy the person or object at first contact, there could be damage resulting from the weight of prolonged material on the objects.
Earthquakes related to volcanism
EarthquakeEarthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s can occur due to volcanic activity. These earthquakes could produce topographical deformation and/or destruction of buildings, homes, cars, etc. There are two different types of these earthquakes: volcano-tectonic earthquakes and long period earthquakes. "Earthquakes produced by stress changes in solid rock due to the injection or withdrawal of magma (molton rock) are called volcano-tectonic earthquakes". These are hazardous due to the possibility of ground cracks or slope failures, therefore destroying everything in its path. Long Period earthquakes, which happen when magma is suddenly forced into the surrounding rocks, are generally seen as a precursor to the actual eruption.
Monitoring and mitigation
According to John Ewert and Ed Miller in a 1995 publication, "a great majority of the world's potentially active volcanoes are unmonitored". Of the historically active volcanoes in the world, less than one fourth are monitored. Only twenty-four volcanoes in the entire world are thoroughly monitored for activity. They also state that "seventy-five percent of the largest explosive eruptions since 1800 occurred at volcanoes that had no previous historical eruptions".The United States Geological Survey is now currently monitoring volcanic activity all around the world. By monitoring the seismic and geological activity, the USGS can warn people ahead of time about impending danger. These volcanologists measure the size of an eruption in two ways: the eruption magnitude (by the volume or mass of magma erupted) and eruption intensity (by the rate of magma erupted). There are also various forms of satellites and imagery, such as satellite InSAR imagery, that monnitor the activity that isn't exposed to the naked eye.
External links
- http://volcanoes.usgs.gov/
- http://www.uwec.edu/jolhm/EH2/Erickson/index.html
- http://www.geo.mtu.edu/volcanoes/hazards/primer/
- http://www.oregongeology.org/sub/earthquakes/volcanoes.htm
- http://vulcan.wr.usgs.gov/Hazards/framework.html