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Home , Eruption column, Lava dome, Lava lake, Magma, Phreatic eruption, Pyroclastic flow

Volcanic Features Information

Caldera

A is a bowl-like volcanic feature usually formed by the collapse of land following a volcanic eruption. They are sometimes confused with volcanic craters. The word comes from Spanish caldera, and this from Latin CALDARIA, meaning "cooking pot". In some texts the English term cauldron is also used.

A collapse is triggered by the emptying of the chamber beneath the , usually as the result of a large volcanic eruption. If enough magma is erupted, the emptied chamber is unable to support the weight of the above it. This causes a roughly circular fracture, the ring fault, to develop around the edge of the chamber. The collapse may occur as the result of a single large eruption, or it may occur in stages as the result of a series of eruptions. The total area that collapses may be hundreds or thousands of square kilometers.

Lava Dome

In the study of volcanoes, a dome is a roughly circular mound-shaped protrusion resulting from the slow leak of thick (high ) lava from a volcano. The geologic chemistry of lava domes can vary from to although most preserved domes tend to have high silica content. The characteristic dome shape is caused by high viscosity that prevents the lava from flowing very far. This high viscosity can occur in one of two ways: by high levels of silica in the magma, or by fluid magma giving off that are dissolved in it.

Pyroclastic Flow

A is a fast-moving current of hot and (collectively known as ), which reaches speeds moving away from a volcano of up to 700 km/h (450 mph). The gas can reach temperatures of about 1,000 °C (1,830 °F). Pyroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope. They are a common and devastating result of certain explosive volcanic eruptions.

Lahar

Lahar is an Indonesian term that describes a hot or cold mixture of water and rock fragments flowing down the slopes of a volcano and (or) river valleys. When moving, a lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay to boulders more than 10 meters (33 feet) in diameter. Eruptions may trigger one or more directly by quickly melting snow and ice on a volcano or ejecting water from a crater . More often, lahars are formed by intense rainfall during or after an eruption--rainwater can easily erode loose and soil on hillsides and in river valleys. Blue Group: Mt St Helens Volcanic Eruption 1980 Where is the volcano?

Mt St Helens (8365 ft , 22,550m) is in the Cascade Volcanic Range in State, USA. The has 160 volcanoes and Mt St Helens is considered the most active, and lies 100 miles south of Seattle and 50 miles from the coast at Portland

Why is there a volcano here?

Mt St Helens is a within the Cascade Volcanic range in Washington State and had been dormant for 100 years prior to 1980. As an Eastern remnant of the Pacific Plate, the Juan da Fuca plate, has subducted beneath continental the Cascade volcanic chain has formed. The Mt.St.Helens volcano has been active for around 40,000 years but the now damaged cone we see today has formed over the last 2,200 years Eruption Style

The volcano is highly explosive and erupts in the Plinian style like Vesuvius. Sudden violent are accompanied by towering clouds of hot ash, dust and rocks thrown high into atmosphere. Pyroclastic flows and volcanic mud flows called Lahars flow down the at speed and consume the surrounding landscape. from basalt to have been erupted forming layers of ash and lava. In many stratovolcanoes a central summit crater has dome of intermediate lava type which is squeezed out of the main vent, similar to Montserrrat. In 1980 this did not occur and instead a crypto dome formed (crypto means hidden) causing the Northern slope of the volcano to bulge and grow. From mapping the deposits around the volcano it seems that lateral blasts and side domes were not unprecedented. Sequence of Events

On May 18 1980 Mt.St.Helens produced an enormous horizontal (sideways) blast which completely destroyed everything for 20 miles north of the volcano. The elevation of mountain peak decreased from 2930m to 2550m and a gaping crater 1.5km wide was created. The sequence of events that occurred had not been witnessed before as until then had always seen volcanoes erupt upwards but this was different this was sideways! In March 1980 and a steam alerted the United State Geologic Survey (USGS) that the volcano was certainly waking up. Throughout the spring the mountain continued to splutter and steam the northern side of the mountain was bulging out by 1.5m/day. A 5 miles exclusion zone was placed around the volcano and famously Harry Truman owner, of the lake lodge resort, refused to leave.

On the morning of May 18 David Johnson was on a ridge 10km north of the volcano when a 5.1 struck. Suddenly the bulge on the north side of the volcano slid downwards in a massive at 300km/hour and crashed into causing an enormous wave of water the rest of the landslide ploughed down the Tootle river valley and mixed with vast quantities of lake water and ice . Davids last message was to his colleagues in the nearby Vancouver USGS base ( not Canada) "Vancouver,Vancouver .. this is it!"

The landslide uncorked the magma in the crypto dome and released the pressure. The gas in the magma instantly expanded and shattered the rocks at supersonic speed creating a lateral of blast ash and hot rocks which overtook the landslide at reached speeds of 1,000km/hour (670 miles/hour) . The blasts power has been estimated at 500 times that of Hiroshima. 600km2 of forest was blown away and trees combed down like hair, sap exploded in trees in the intense heat. Trees up to 20 miles away were engulfed in the blast 4 times the distance of the exclusion zone.

The third string to Mt.St.Helens bow was a 19km (12miles) high eruption cloud which powered vertically out of the volcano in a matter of minutes. The cloud turned day to night and ash fall was heavy. Lightning crackled around the cloud.

Mudflows or Lahars formed within minutes of the eruption. lake water, melted glacier ice, hot ash and debris all combined to send hot ( 29-33C) cement like flows down the Toutle river. Pyroclastic flows started to form from the crater just after the blast as fresh magma came into contact with the air. Material appeared to overflow the craters edge and flow down the Toutle valley as a grey turbulent cloud.

Harry Truman and David Johnson along with 55 other people did not survive. Both have had ridges named after then within the Mt.St.Helens national monument. The area within the monument is being left to recover naturally. Within 8km of the volcano all trees were obliterated, from 8km to 30km flattened and outside this dead but left standing. Outside the boundary logging companies have replanted trees.

Mount St. Helens showed significant activity on March 8, 2005, when a 36,000-foot (11,000 m) plume of steam and ash emerged. A new dome is growing and will eventually fill the 1980 crater. Effects and Aftermath

Rescue helicopters looking for survivors were grounded or could not land due to ash. Ash removal from roofs and roads was costly and lengthy costing 2 million dollars just in one town(Yakima) Hazard Management

All volcanoes in the Cascades are monitored by the Cascades Volcanic Observatory CVO part of the Geological Survey USGS from their base in Vancouver, not Canada but Washington State USA. On March 27th 1980 a signaled the beginning of an active phase. The CVO moved in a team of Geologists to monitor the volcano. Small eruptions of steam and ash blasted from the old summit dome continued and attracted attention from the press and tourists. Evacuation plans were prepared and roads closed leading to the volcano. As the mountain swelled with magma, and bulged outwards at a rate of 1.5m/day, it was obvious that the Spirit Lake area to the north of the volcano needed to be evacuated. The Washington State Governor placed a 5 mile red zone around the summit only Harry Truman an 83 year old resort owner refused to move. When the volcano erupted on May 18th the lateral blast extended 20 miles 4 x the exclusion zone.

Red Group: Kilauea Volcano Where is the volcano?

Located in the south of the Big Island within the Hawaii Volcanoes National Park. Kilauea sits on the shoulder of and the summit is only 1247m (4091ft). There are no steep slopes here as this is a volcano and slopes are very low angled and gentle due to successive lava flows. Kilauea has been active for 23,000 years and has been continuously erupting since 1983 ; 90% of the volcano is less than 1,100 years old. The summit caldera is around 11 miles in circumference and contains the Halema'uma'u crater (active 1974), the home of , and the Kilauea Iki (little Kilauea) crater which was active in 1959. The floor of the caldera contains lava flows from the 1970s and 1980s, the most recent being lava from 1982.

The Pu'u' oo ( "Poo-oo Oh Oh") vent on the southern slope of the volcano ,along the south eastern zone,is the site of current activity and first became active in 1983 with lava fountains 460m high. When has Kilauea erupted?

Kilauea first emerged from the floor around 500 000 years ago as the next in the Hawaiian chain of volcanoes. There have been 61 historical eruptions with the oldest dated rocks being 23,000 years old. Since 1952 there have been 34 eruptions and Kilauea has been erupting continually since 1983. Firstly with the eruption of Pu oo oo vent and now from the Kamoamoa Fissure which erupted in March 2011 generating 2.5million cubic meters of lava/day. In 1990 the towns of Kalapana and Kaimu were totally destroyed by lava flows from the Kupaianaha vent plus a long stretch of Route 130,the coastal road, which now abruptly dead-ends at the lava flow.50 ft of lava covers the towns. Homes have also been destroyed in 2008,2010 and 2011. In March 2008 the summit crater of Halema'uma'u produced its first explosive event since 1924, showering the summit area in debris and causing the closure of roads to tourists. In 2011 the crater has a within a collapsed section of the cater floor. Why is there a volcano here?

Hawaiian volcanic activity is due to a Mid-ocean Hot Spot or plume firing a jet of hot rock at the base of the Pacific Ocean over the past 70million years to form the Hawaiin-Emperor Semount chain . The jet of hot rock punches a hole through the crust and creates a volcano which eventually emerges from the ocean as an island. As the Pacific plate has moved to the NW over the Hot Spot at a rate of 5-10cm /year, islands have moved away from the Hot Spot and new volcanic islands have been created. The older volcanic islands erode until they become coral atolls and eventually disappear beneath the waves to become sea mounts. The entire chain is 5000km long the oldest sea mount being near the Aleutian trench near Alaska and the youngest volcano is Lo'ihi, which is still submerged off the coast of Big Island( Hawaii Island). Eruption Style

Hawaiian volcanoes erupt basaltic lava which has low viscosity and erupts at around 1000C. Most eruptions are gentle effusive lava flows which can travel far from the vent. Spectacular lava fountains can also be produced, as in the Kilauea Iki eruption of 1959 which reached 320m high. Hazard Management

The volcano is monitored by the United States Geological Survey (USGS) who have an observatory on the Kilauea crater rim. Lava flows are the main and VOG- volcanic gases mixing with clouds or steam. Lava flows are currently flowing from Kilauea but it is Mauna Loa which poses the biggest risk to the largest settlement in the South- Hilo. Currently lava flow hazard areas are mainly on the south and south east coast. Hawaii is also prone to which originate from around the Pacific Ring of . Tsunamis from (1960), Alaska (1949/64) and . The Pacific Warning Centre is located in a on Oahu. Key to map here.

Hawaii volcano observatory

Black Group: Volcanic Eruptions / Soufriere Hills Volcano Where is the volcano?

The Soufriere Hills volcano lies in the small Island of Montserrat in the Antilles Islands. The Island is a British Protectorate and lies to the SW of Antiqua. The Island at its largest is no more that 12km by 8km and before the eruption had a population of 11000.

When was this eruption?

The current eruptive phase began on 18th July 1995 when large billowing clouds of ash and steam erupted from Soufriere Hills volcano in the south of the island. The eruption has left the southern two thirds of the island uninhabitable and it remains so to this day. Pyroclastic Flows still pour down the slopes of he volcano. Check out the latest eruptions at the MVO- Montserrat Volcanic Observatory Why is there a volcano here?

The Soufriere Hills volcano is situated above a destructive plate margin, or zone which forms the Peurto Rico Trench. from the North American plate is sinking under the Caribbean plate, forming the Antilles volcanic . As the slab of crust descends, , water and the heat of the mantle cause the wedge of mantle above the slab to melt. The molten rock is less dense than the surrounding crust and rises to the surface. The magma formed at a depth of around 6km, with a temperature of 820–885°C, and then partially crystallized before a new injection of deep magma boosted it towards the surface.

At the surface, a thick viscous dome of lava appeared in English’s Crater in the Soufriere Hills. Most of the gas in the lava had already escaped but some remained in pockets, which caused explosive eruptions.

The volcano is a strato volcano, composed mainly of consolidated ash layers from previous eruptions. Initially pyroclastic flows flowed eastwards from the open crater down the Tar River valley, but as the dome grew, eventually flows were able to come down any side of the volcano. The flows particularly followed four main river valleys: Tar River, White River, Mosquito Ghaut and Fort Ghaut. Where the flows reached the sea they created new deltas of land e.g. Tar River valley delta. Eruption Style

The volcano is a strato-volcano . Pyroclastic Flows and eruption columns characterize the Soufriere Hills volcano . Such flows occur when the dome collapses or explodes. Tonnes of hot rock, lava and ash explode from the crater in a fast-moving cloud. The cloud can race straight down the mountainside, or if there is a large vertical , which creates an ash column, come crashing down as the ash column collapses. Such clouds have two parts: on the ground, an of large boulders and rocks, and above this a cloud of ash and gas with temperatures of 400°C+. The cloud moves at speeds of 100mph, obliterating and incinerating everything in its path.

Sequence of Events

 1992/1994 Earthquake swarms first detected  1995 July Phreatic eruption of ash and steam August 5,000 evacuated as a precaution December Plymouth evacuated as new dome grows.  1995 Nov New dome grows  1996 January English’s Crater and rapidly buries old dome. Residents allowed to return during quiet phase. March–Sept First pyroclastic flows down the Tar River valley, creating a new delta in the sea. April South of island evacuated. Plymouth abandoned.  1997 June 25/6 Most devastating flow yet down NE slopes of volcano. 19 people killed who had returned to their homes in the danger zone.9000m high eruption cloud.  1997 August Pyroclastic flows destroy Plymouth, Montserrat’s capital 3 miles from crater. Permanent relocation of inhabitants away from island is considered by British government. Exclusion zone expanded, residents advised to seek shelter, wear helmets and masks outdoors. Warning of cataclysmic eruption.  1997 September Montserrat’s Volcanic Observatory advises all residents to move as far north as possible immediately. 5,000 now live in shelters. Flows destroy Bramble airport 3.5 miles from crater. People may be moved forcibly from the exclusion zone.  1997 October Eruptions approximately every 9 hours. Ash and tephra land in safe zone. Dome is 250ft above old crater and growing at 280ft3/second.  1997 November Dome collapse remains a threat, causing large eruptions.  1997 December Boxing Day eruption. Pyroclastic flows down the White River valley. Eruption clouds to 36,000ft.  1999 July 20 Large eruption from dome collapse. Eruption cloud to 35,000 ft. Threat of dome collapse is still real. People largely out of danger unless in the exclusion zone. Restructuring of the north continues.

Effects and Aftermath

Montserrat’s population have had their lives completely changed. Their economic, administrative and cultural capital lies in ruins like a modern . Jobs, schools and community activities have been disrupted. At one point 5,000 people were living in temporary shelters in the north, in some cases for over two years. The north of the island had few settlements of any size and found it difficult to cope with the influx from the south. Salem is now being repopulated and is being developed together with St Johns as new population centers. The following are some of the problems:

 Plymouth contained all the main services – hospitals, banks, schools, government and many private businesses.  collapse of the tourist and rice processing industries  unemployment has risen from 7% to 50%.  agriculture is at a standstill. • respiratory problems caused by ash.  psychological problems and discontent with relocation package  traffic congestion  shortage of available building land  70% rise in rent for accommodation  skills shortage as people left. Hazard Management

Once the volcano was deemed dangerous to life. Evacuations plans and Hazard maps were put into place. The maps contained areas of increasing risk including the highest risk area- the exclusion zone. As the eruption progressed the zones were modified until the southern two thirds of the island was declared an exclusion zone. Monitoring

 An extensive seismograph network was established around the volcano to measure earthquake strength and depth.  deformation meters and tiltmeters were also put in place to show any signs of the ground swelling or deflating as magma rose within the volcano.  A satellite location GPS (global positioning system) was also used to check ground movements.  An instrument called COSPEC was used to measure gas emissions from the volcano, particularly sulphur dioxide which is a good indicator of magma type and movement.  The pH of rainwater was monitored as it gives an indication of the magmatic gas content.  Geologists regularly flew into the most dangerous areas to sample new flow deposits, measure cracks caused by the volcano swelling and check the growth of the dome.