Custom papers academic service


Primary and secondary hazards of volcanic eruptions

Volcanic Hazards

Many types of hazards are associated with volcanoes Article by Jessica Ball Lava Flows This is one of several lava streams of the Prince Avenue flow slicing through the forest between the cross streets of Paradise and Orchid.

The lava stream is about 3 meters 10 feet wide. Enlarge Image Volcanic Hazards Volcanoes can be exciting and fascinating, but also very dangerous. Any kind of volcano is capable of creating harmful or deadly phenomena, whether during an eruption or a period of quiescence.

  1. Early detection gives the maximum amount of time for people to prepare for an eruption. Most of the time, these processes are faulting and fracturing that does not lead to an eruption.
  2. However, they can cause massive damage to land and property and trigger fires.
  3. The event is defined and a hazard assessment is conducted regularly. Volcanic Gases All magmas contain dissolved gases that are released during and between eruptive episodes.
  4. Yet the Yellowstone system is still active. Most of the damage caused by falls occurs when wet ash and scoria on the roofs of buildings causes them to collapse.
  5. Seismicity Earthquakes commonly provide the earliest warning of volcanic unrest, and earthquake swarms immediately precede most volcanic eruptions.

Understanding what a volcano can do is the first step in mitigating volcanic hazards, but it is important to remember that even if scientists have studied a volcano for decades, they do not necessarily know everything it is capable of.

Volcanoes are natural systems, and always have some element of unpredictability. Volcanologists are always working to understand how volcanic hazards behave, and what can be done to avoid them.

Primary and secondary hazards of volcanic eruptions are a few of the more common hazards, and some of the ways that they are formed and behave. Please note that this is intended as a source of basic information only, and should not be treated as a survival guide by those who live near a volcano.

Always listen to the warnings and information issued by your local volcanologists and civil authorities. Lava Flows Lava is molten rock that flows out of a volcano or volcanic vent. Depending on its composition and temperature, lava can be very fluid or very sticky viscous. Fluid flows are hotter and move the fastest; they can form streams or rivers, or spread out across the landscape in lobes.

Viscous flows are cooler and travel shorter distances, and can sometimes build up into lava domes or plugs; collapses of flow fronts or domes can form pyroclastic density currents discussed later. Most lava flows can be easily avoided by a person on foot, since they don't move much faster than walking speed, but a lava flow usually cannot be stopped or diverted. Lava flowing from a vent also creates enormous amounts of pressure, which can crush or bury whatever survives being burned.

Pyroclastic Density Currents Pyroclastic flow deposits covering the old city of Plymouth on the Caribbean island of Montserrat.

Helens, Washington, August 7, 1980.

What is the difference between a primary and a secondary effect of a natural disaster?

Enlarge Image Pyroclastic Density Currents Pyroclastic density currents are an explosive eruptive phenomenon. They are mixtures of pulverized rock, ash, and hot gases, and can move at speeds of hundreds of miles per hour.

These currents can be dilute, as in pyroclastic surges, or concentrated, as in pyroclastic flows. They are gravity-driven, which means that they flow down slopes. A pyroclastic surge is a dilute, turbulent density current that usually forms when magma interacts explosively with water. Surges can travel over obstacles like valley walls, and leave thin deposits of ash and rock that drape over topography. A pyroclastic flow is a concentrated avalanche of material, often from a collapse of a lava dome or eruption column, which creates massive deposits that range in size from ash to boulders.

Pyroclastic flows are more likely to follow valleys and other depressions, and their deposits infill this topography.

Occasionally, however, the top part of a pyroclastic flow cloud which is mostly ash will detach from the flow and travel primary and secondary hazards of volcanic eruptions its own as a surge. Pyroclastic density currents of any kind are deadly. They can travel short distances or hundreds of miles from their source, and move at speeds of up to 1,000 kph 650 mph.

The speed and force of a pyroclastic density current, combined with its heat, mean that these volcanic phenomena usually destroy anything in their path, either by burning or crushing or both. Anything caught in a pyroclastic density current would be severely burned and pummeled by debris including remnants of whatever the flow traveled over.

There is no way to escape a pyroclastic density current other than not being there when it happens! One unfortunate example of the destruction caused by pyroclastic density currents is the abandoned city of Plymouth on the Caribbean island of Montserrat.

That part of the island has since been declared a no-entry zone and evacuated, although it is still possible to see the remains of buildings which have been knocked over and buried, and objects that have been melted by the heat of the pyroclastic density currents. Pyroclastic Falls Mount Pinatubo, Philippines. Cubi Point Naval Air Station. USN photo by R. Enlarge Image Pyroclastic Falls Pyroclastic falls, also known as volcanic fallout, occur when tephra - fragmented rock ranging in size from mm to tens of cm fractions of inches to feet - is ejected from a volcanic vent during an eruption and falls to the ground some distance away from the vent.

Falls are usually associated with Plinian eruptive columns, ash clouds or volcanic plumes. Tephra in pyroclastic fall deposits may have been transported only a short distance from the vent a few meters to several kmor, if it is injected into the upper atmosphere, may circle the globe.

Any kind of pyroclastic fall deposit will mantle or drape itself over the landscape, and will decrease in both size and thickness the farther away it is from its source. Tephra falls are usually not directly dangerous unless a person is close enough to an eruption to be struck by larger fragments. The effects of falls can be, however.

  • What were the long term effects of each of these eruptions on the global environment?
  • This caused worldwide incidences of extreme weather, and led 1816 to be known as 'The Year Without A Summer;
  • In the event of an emergency, the Government is authorised to issue special instructions in relation to general traffic, rules and safety in official places and areas to which the public has access;
  • During the May 1980 eruption at least 17 separate pyroclastic flows descended the flanks of Mount Saint Helens;
  • They can travel short distances or hundreds of miles from their source, and move at speeds of up to 1,000 kph 650 mph;
  • The Diagram below illustrates the how the plates diverge.

Ash can smother vegetation, destroy moving parts in motors and engines especially in aircraftand scratch surfaces. Scoria and small bombs can break delicate objects, dent metals and become embedded in wood.

Some pyroclastic falls contain toxic chemicals that can be absorbed into plants and local water supplies, which can be dangerous for both people and livestock.

The main danger of pyroclastic falls is their weight: Most of the damage caused by falls occurs when wet ash and scoria on the roofs of buildings causes them to collapse. Pyroclastic material injected into the atmosphere may have global as well as local consequences. When the volume of an eruption cloud is large enough, and the cloud is spread far enough by wind, pyroclastic material may actually block sunlight and cause temporary cooling of the Earth's surface.

Following the eruption of Mount Tambora in 1815, so much pyroclastic material reached and remained in the Earth's atmosphere that global temperatures dropped an average of about 0.

Module 6 - Volcanoes

This caused worldwide incidences of extreme weather, and led 1816 to be known as 'The Year Without A Summer. Enlarge Image Lahars Lahars are a specific kind of mudflow made up of volcanic debris. They can form in a number of situations: Lahars flow like liquids, but because they contain suspended material, they usually have a consistency similar to wet concrete.

They flow downhill and will follow depressions and valleys, but they can spread out if they reach a flat area. Lahars can travel at speeds of over 80 kph 50 mph and reach distances dozens of miles from their source. Lahars are not as fast or hot as other volcanic hazards, but they are extremely destructive.

Hazards associated with volcanic eruptions Flashcards Preview

They will either bulldoze or bury anything in their path, sometimes in deposits dozens of feet thick. Whatever cannot get out of a lahar's path will either be swept away or buried. Lahars can, however, be detected in advance by acoustic sound monitors, which gives people time to reach high ground; they can also sometimes be channeled away from buildings and people by concrete barriers, although it is impossible to stop them completely.

Dead cattle and surrounding compounds in Nyos village. Photo copyright Jessica Ball. Enlarge Image Gases Volcanic gases are probably the least showy part of a volcanic eruption, but they can be primary and secondary hazards of volcanic eruptions of an eruption's most deadly effects.

Most of the gas released in an eruption is water vapor H2Oand relatively harmless, but volcanoes also produce carbon dioxide CO2sulfur dioxide SO2hydrogen sulfide H2Sfluorine gas F2hydrogen fluoride HFand other gases. All of these gases can be hazardous - even deadly - in the right conditions. Carbon dioxide is not poisonous, but it displaces normal oxygen-bearing air, and is odorless and colorless.

Because it is heavier than air, it collects in depressions and can suffocate people and animals who wander into pockets where it has displaced normal air. It can also become dissolved in water and collect in lake bottoms; in some situations, the water in those lakes can suddenly 'erupt' huge bubbles of carbon dioxide, killing vegetation, livestock and people living nearby.

About the author

This was the case in the overturn of Lake Nyos in Cameroon, Africa in 1986, where an eruption of CO2 from the lake suffocated more than 1,700 people and 3,500 livestock in nearby villages. Sulfur dioxide and hydrogen sulfide are both sulfur -based gases, and unlike carbon dioxide, have a distinct acidic, rotten-egg smell. SO2 can combine with water vapor in the air to form sulfuric acid H2SO4a corrosive acid; H2S is also very acidic, and extremely poisonous even in small amounts.

Both acids irritate soft tissues eyes, nose, throat, lungs, etc.

Hazardous Volcanic Events

If sulfur-based aerosols reach the upper atmosphere, they can block sunlight and interfere with ozone, which have both short and long-term effects on climate. One of the nastiest, although less common gases released by volcanoes is fluorine gas F2. This gas is yellowish brown, corrosive and extremely poisonous. Like CO2, it is denser than air and tends to collect in low areas. Its companion acid, hydrogen fluoride HFis highly corrosive and toxic, and causes terrible internal burns and attacks calcium in the skeletal system.

  1. In New England, the year following the eruption has come to be known as "The Year Without a Summer" because of widespread snow and killing frosts in June, July, and August of that year. Recent caldera forming eruptions, their location, and volume of magma erupted.
  2. They can travel over 80 kilometers and commonly reach speeds of 35 to 65 kilometers per hour.
  3. Understanding what a volcano can do is the first step in mitigating volcanic hazards, but it is important to remember that even if scientists have studied a volcano for decades, they do not necessarily know everything it is capable of.
  4. In the event of an emergency, the Government is authorised to issue special instructions in relation to general traffic, rules and safety in official places and areas to which the public has access. Three major caldera systems are found in North America.

Even after visible gas or acid has dissipated, fluorine can be absorbed into plants, and may be able to poison people and animals for long periods following an eruption.

After the 1783 eruption of Laki in Iceland, fluorine poisoning and famine caused the deaths of more than half the country's livestock and almost a quarter of its population. Volcanic Hazard Resources Bardintzeff, J.

Environmental Geology - Geol 406/506

Berlin, Springer, 324 p. Her concentration is in volcanology, and she is currently researching lava dome collapses and pyroclastic flows.

She also writes the Magma Cum Laude blogand in what spare time she has left, she enjoys rock climbing and playing various stringed instruments.