Volcano Top 20 Frequently asked questions.
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A volcano is an opening , known as a vent, through which molten rock, ash( minute particles of rock) and gases are erupted onto the earths surface.Volcanoes can erupt onto land or beneath the sea.
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Volcanoes occur along plate boundaries or within plates - intraplate. See Plate Tectonics
Volcanoes form over subduction zones or destructive boundaries, where one plate is subducted beneath another causing melting of the mantle above. The melt or magma rises to the surface through weaknesses in the earths crust where it erupts typically as a strato volcano.
Volcanoes also occur at Mid Ocean Ridges or Constructive Boundaries where oceanic crust is being created. As two oceanic plates pull apart magma rises to the rift where the plates are pulling away from each other.Basaltic pillow lavas are erupted to form the ocean floor from gabbro magma chambers. Long under water chains of volcanoes snake across the floors of the oceans hidden from view.
Volcanoes also occur in intra-plate settings, in the middle of a plate. A mantle plume, or hot spot, is a jet of hot rock straight from the mantle which pierces the crust crust above. Hawaii s volcanoes are formed in this way, the chain of islands form as the overlying plate moves over the hot spot. Under a continent a hot spot can initiate rifting, as occured with the Iceland plume initiating the opening of the North Atlantic. A plume underlies Yellowstone and is responsible for the enormous caldera eruptions that have occured here in the past.
The most volcanoes on land occur around the Pacific Ring of Fire but the oceans hide the majority of the worlds volcanoes beneath the waves along Mid Ocean Ridges.
Volcanoes and earthquakes both occur where there is plate tectonic activity. Earthquakes occur where volcanoes occur either caused by tectonic plate movements , as at a destructive plate boundary,or by movement of magma within the crust. Earthquakes occur due to fault movements and can occur away from volcanoes at conservative plate margins, collision zones or anywhere there are crustal movements.
Earthquakes occur where we get volcanoes but earthquakes dont need volcanoes to happen!
More in Plate Tectonics.
More in Top ten highest volcanoes. and Highest volcanoes by continent Mauna Loa from the sea floor to its summit is 9000m making it the highest mountain on earth ( Everest has the highest mountain summit). Mauna Loa has erupted lava totaling 17 000 feet and is do heavy it has depressed the earths crust.It is the largest volcano on earth. 10 Largest eruptions Kilauea is regarded as the most active volcano at the present time as it has erupted more lava than any other volcano currently erupting. Stromboli has been continually (most days) erupting for at least the last 2000 years and Etna the last 3500 years.
More in 10 most active volcanoes
If we take eruptions in the last 10 000 years there are probably 1500 volcanoes in the world which have erupted.75% of the worlds active volcanoes are in the" Ring of Fire" around the Pacific Ocean (see below). Between 50 and 70 erupt each year and around 160 per decade. These figures just concern land volcanoes. Three quarters of lava erupted does so beneath the sea at constructive boundaries/ mid ocean ridges where new oceanic crust is created.
More in Number of volcanoes by country
Indonesia lays claim to the two largest eruptions we know of. Tambora is a stratovolcano and on April 10 1815 erupted 100 km3 of material and was heard 1200 miles away. The followig summer of 1816 became known as the "Year without a summer" and caused crop failure and famine in Europe and North America.
In pre history 72000 years ago the Supervolcano Toba
2800 km3 of material formig a caldera 100km by 30km , the largest known eruption in the last 25 million years.Which affected the earths climate so much that mankind was nearly wiped out. The Volcanic winter that followed may have lowered the earths average temperature by 4C and 15C in higher latitudes. Some theories say the eruption initiated the next cold stage of the ice ages some say it did not.
More in 10 largest eruptions in the last 10 000BC and Largest Ancient eruptions we know of.
Indonesia has the most active volcanoes in the world. Around 127 active volcanoes .More in Number of volcanoes by country
The Pacific Ring of Fire is 25,000 mile long horse shoe shaped zone of volcanoes, earthquakes and fault lines which loops round the western,northern and eastern Pacific Ocean.The Pacific Ocean crust is being subducted and destroyed beneath the surrounding continents and other oceanic plates along a nearly continuous destructive boundary Deep trenches occur where the descending oceanic crust sinks beneath overriding plate, including the Marianas trench which is 6.831 miles deep. The Volcanoes of The Andes, Mexico,The Cascades, The Aleutians, Kamchatka Peninsular,Japan,Indonesia ,The Phillipines and New Zealand are on the Pacific ring of fire. 75% / 450 of the worlds volcanoes are located here. In New Zealands south island and California the tectonic plates move past each other causing earthquakes but no volcanoes.
The volcanoes in Hawaii are at the end of Hawaiian Emporer Seamount Chain, a 3600 miles long chain of volcanoes which stretches across the Pacific.There are 8 main islands and several islets.
The Volcanoes of Hawaii are caused by a mantle plume or hotspot, which is a jet of hot magma from deep in the mantle. The plume pierces the Pacific oceanic crust above causing large quantities of basaltic lava to be erupted on the ocean floor forming volcanoes. Eventually the volcano breaks the surface and keeps growing as long as the magma supply continues. Mauna Loa,on Hawaii s Big Island is earths largest volcano, and measures 9000m from base to summit. It has erupted 17 000 feet of lava and has such a great mass it has depressed the earths crust. Current volcanic activity in Hawaii is from Kilauea and a new island offshore called Loihi which should emerge in 50 000 years time.
The Pacific plate is moving over the hot spot at 32 miles/million years, and as it moves it carries the islands above with it and away from the hotspot. This creates a chain of islands which eventually erode and form an underwater chain of seamounts under the sea. More on Hawaiian Volcanoes here.
Britain has quite a few ancient volcanoes. The Lake District,Snowdonia,the islands of North West Scotland such as Skye and Mull and the Giants Causeway of N Ireland are all volcanic. Arturs Seat in Edinburgh and Edinbugh castle itself owe there lofty heights to ancient volcanoes.
There have been three phases of volcanic activity. Firstly during the Ordivician period (443ma to 495ma) an Ocean called Iapetus seperated Scotland from England and Wales.At the end of the Ordovician the subduction occured and started to close the ocean. his caused volcanic activity in the Lake District and Snowdonia. This event is called the Caledonian Orogeny and the mountain remnenats from this event can be found in the Appalachians,Scotland and Norway. The final closure of Iapetus created the Southern Uplands of Scotland.
A second phase of volcanic activity occured during the Devonian (395Ma) to end of the Lower Carboniferous (325Ma). After the Caledonian mountain range had been formed a rift valley formed through central Scotland . It is likely this formed from post collisioal sagging and relaxing of the crust. Volcanic activity created Arthurs seat,Dundee Law and Stirling castle Crags.
The third phase of volcanic activity began 60Ma ago in the Tertiary. At this time Britain was still joined to North America and Greenland. A hot spot under present day Iceland initiated rifting and the breaking away of North America from Europe and the opening of the North Atlantic. Basaltic volcanism occured and formed the volcanic rocks of present day Skye,Mull,Ardnamurchan and the flood basalts of the Giants Causeway.
Geologists have more success with volcano prediction than earthquake prediction and there have been succesful predictions which have saved lives. Seismc monitoring, gas monoring and deformation studies are the three key areas of monitoring that volcanologists use.Seismic monitoring indicates whether magma is moving within the volcano.Gas monitoring ,particularly sulphur dioxide,can tell us about the magma in the volcano.Ground deformation studies can tell us if the volcano is inflatingas magma feeds into the volcano or deflating as it drains away. Volcanologists also look at past history of eruptions to try to assess what will come next time. Monitoring and Prediction
Recent research by Bernard Chouet of the USGS discovered the importance of Harmonic tremors , continuous rhythmic earthquakes that can be detected by seismographs. Harmonic tremors often precede or accompany volcanic eruptions. The tremors are long seismic events of the same frequency which indicate the movement of magmaor release of gas in the volcano. December 2000 saw the successful prediction of an eruption of Popocatapetl within 2 days. The localpopulation was evacuated successfully. This was Chouets work.Top man!Volcano World Article on predicting volcanoes
Volcanoes can pose immendiate risk to local inhabitants and it tends to be large explosive eruptions,lahars and tsunamis which cause the greatest loss of life from the immediate effects of a volcanic eruption. Tambora in 1815 is thought to have directly killed 92,000 people. Supervolcano eruptions such as Yellowstone or Toba have global consequences which cause climatic changes . These would affect crop production, global temperatures and sunlight levels which have had (Toba) and would have serious implications for the whole planet. More on the most deadly volcanoes
Effusive basaltic eruptions ,such as in Hawaii, have little danger to people however large flood basalt events would do.
Volcanologists differ on these terms but generally
Active: likely to erupt,continuous activity,earthquake activity,magma supply,high heat flow
Dormant : No recent eruption, no written record of eruption, but signs the volcano is not extenct
Extinct : No activity of any kind for 1000 s of years.
The Hollywood images of rivers of lava flowing from volcanoes makes a dramatic scene. However not all volcanoes erupt rivers of lava. All active volcanoes have a magma chamber but not all will erupt a lava flow, it depends on the magma type. Shield volcanoes erupt basaltic lava ,from a gabbro melt, which flows as either the fluid pahoehoe or aa-aa ,a blocky lava flow. This lava is low in silica which reduces its viscosity.
The steeper sided stratovolcano will erupt a mixture of lava and ash. The magma here can range from andesite-dacite or even rhyolite, increasing silica % makes the lava more viscous and potentially explosive. Andesite lava will flow, dacite lava is often extruded as a dome, rhyolite lavas can also disguise themselves as pumice or obsidian . Volcanic Rock Types
In summary. The more silica the stickier the lava, the more likely the volcano will erupt explosiviely blasting the magma and potential lava into ash. Runny lava is basaltic and best seen in Hawaii, Etna or Stromboli.Although Rhyolite breaks the rule and can flow for 10s km at 950 C.
Lava is not especially dangerous to human life but can cause unpreventable destruction to property,ecosystems and farmland. Basaltic lava erupts at around 1000 C, andesite lava at around 800 C,rhyollite 700 C. Rhyolite unusually can flow a 10s Km and reach temperatures of 950 C. More on Lava as a Volcanic Hazard
500 million people live near volcanoes in the world. Seattle is near Rainier, Mexico city is near Popocatapetl .
Naples, a city of 3.5 million sprawls on the lower slopes of Vesuvius,a volcano which is certainly very active and very dangerous. Naples is a city living in a hazardous position but situated by the sparkling mediterranean,with sunshine and the good italian life the local population live on borrowed time.
Perception is very important in peoples response to natural hazards,I have put it as number one reason. If the volcano has not erupted recently then people live in denial and hope of no more activity.The "It won t happen to me "is avery strong motivator to stay put. Just how the local authorities could evacuate up to 5 million people safely and quickly is something even the authorities are still perplexed about.Everyone is crossing their Italian fingers on this one. Volcanic Hazard Management
Perceptions of risk
It won't happen here , It won't happen to me , I'd get away,It's not that dangerous,We have a great life,My family is here,I belong here,My livelyhood is here, What do scientists know any way. The mountain won't hurt me.
Agriculture / soil fertility
The slopes of volcanoes are fertile and grow very good crops. Farming communities develop round volcanoes if the climate is right ie.Indonesia,Etna
Cultural and communities associated with the volcano.
Economic conditions prevent a move away.
It won't erupt again so soon
The volcano has not erupted recently and is dormant.
Iceland makes 2/3 rds of it electricty from steam powered turbines.
Mineral wealth and mining
Metallic minerals Gold,Silver,Copper,Lead and Sulphur
Attracts visitors and wealth.
Its a beautiful place to live
Attempts have been made to divert lava flows with some success.
On Heimay,a small Island off the Icelandic coast, at 1.55am on the 23 January 1973 a fissure 1800m long opened up from one shore to the other. A curtain of fire and lava shot into the air 200m only 1km from the only town of Vestmannaeyjir. The population were evacuated by the fishing fleet. Houses were soon buried in tephra and the lava started advancing towards the towns harbour which was vital for the towns fishing fleet and livelyhood. The population were determined to save their harbour and pumped millions of tonnes of sea water onto the advancing lava front to cool the advancing flow. It worked and the lava flow in the end enhanced the harbour entrance.
Lava flows have been threatening towns on Mt Etna for hundreds of years. Attempts were often made to divert lava flows but it was banned in the end because other towns were being put at risk.Recently however now that the authorities have control successful attempts have been made most notably in 1983 and 1991.In 1935 the US Army bombed a lava flow from Mauna Loa which was threatening Hilo on Big Island. The flow eventually stopped short but whether it was the bombs or the offerings to Pele is up for debate.
Volcanoes have a significant and frquently overlooked influence on our climate. Volcanoes release ash and gases which if released on a large enough scale can affect the climate of the entire planet.
Sulphur dioxide released as tiny droplets forms sulphuric acid when it combines with water in the atmosphere. This haze or aerosol cloud causes global cooling as it reflects the suns energy back into space. The Sulphur dioxide also destroys ozone which protects the earth from harmful UV radiation.
The eruption of Pinatubo on June 15 th 1991 ejected 20 million tonnes of sulphur dioxide 20 miles up into the atmosphere. The eruption cooled the earths atmosphere lasted 3 years and reached up to 1.3 degrees. The Laki eruptions on Iceland caused a "blue haze" over europe which caused a severe winter in 1783-1784. Tambora 1815 and Kilauea also had similar effects.
Large Ash clouds can cause cooling but the effect does not last as long as the ash falls out from the atmsphere.Carbon dioxide is released by volcanoes, but human activity releases more, so volcanoes are not too blame for global warmimg.
In Europe the best place to see red hot lava is either on Mt Etna or Stromboli.Lava fountains regularly from both.
Check here for activity
In the USA your best chance is on the slopes of Kilauea either by viewing lava flowing into the sea or taking a flight and seeing the lava from above. The Kilauea crater potentially has a lava lake but access is restricted. Check here for activity.
Villarica in Chile has a lava lake. Pacaya volcano in Guetamala is set up for visitors. Mt Erebus in Antartica not really a viable tourist trip.
Erta Ale in Ethiopia and Nyiragongoin the Democratic Republic of Congo have lava lakes but go with an organised and experienced trip.