Volcanic Hazard Management
Volcanic Hazards fall under Geological and Geomorphological Hazards. Although volcanic eruptions are more predictable than earthquakes, there is very little if anything that man can do to prevent or alter the hazardous events happening. The only events people can occasionally have control over are the diversion of lava flows,lahars and lake gas. Ashfall,pyroclastic flows,fountaining,lava eruptions and lahars cannot be prevented from happening. It is how the risk is decreased to people that is the main strategy of volcanic hazard management.
The main Strategy for preserving lives in the event of an eruption is Public Information.
- Public Preperation: making sure the public are prepared and know what to do before,during and after and eruption.
- Establish evacuation centres,routes and logistics
- Put out information on TV,radio or if need be personal contact
- Drills and Sirens
- Clear up teams
- Co-ordination of emergency Services
- Exclusion Zones
- Hazard and risk maps and land use planning.
Monitoring and Prediction
Monitoring of volcanoes has led to increasing success in predicting volcanic eruptions. The United States,Italy and Japan are the leaders in this field. See the monitoring TAB for more.
Sakurajima is possibly one of the most monitored volcanoes on earth. The Sakurajima Volcano lies near Kagoshima City, which has a population of 500,000 people. Both the Japanese Meteorological Agency (JMA) and Kyoto University Sakurajima Volcanological Observatory (SVO) monitors the volcano's activity.The volcano has been recently active since 1995 but no lava.The following show how Japan has learnt to monitor and predict the volcano. The following pattern of observations have been shown to be a precursor to an eruption at Sakurajima.
- swelling of the land around the volcano as magma below begins to build up.
- Earthquakes between 2-5km below the surface shows that magma is pushing upwards.Sak* has a tunnel deep into the mountain to measre the earthquakes.
- Bore holes with temperature sensors detect rises in temperaure. The amount of HCl and released SO2 increases , remote sensing is used to monitir the gases.
- The Sakursjima Volcanic Observatory s network of tiltmeters detect every movement of the mountain, even the smallest movement can herald and eruption.
- Seismometers detect earthquakes which occur immediately beneath the crater, signaling the onset of the eruption. They occur 1 to 1.5 seconds before the explosion.
One of the leaders in eruption prediction is Bernard Chouet who has pioneered a technique of looking at long period earthquakes (harmonic tremors)beneath a volcano which are the result of gas being pressurised within the volcanoes plumbing. His theory was put to the test when the Mexican authorities evacuated 10s of 1000s of people away from Popocatepetl based on the prediction that there woud be an eruption in 2 days time. He was right, the eruption happened and noone was hurt. After the disaster at Armero caused by Nevado del Ruiz where warning signs had been disregarded this was a great success.
Soufriere Hills Volcano Montserrat
The small Caribbean Island of Montserrat is a good example of Managing the risk posed by a volcanic eruption. Montserrat is a small island(7x3 miles) from 1995 onwards the Soufriere Hills Volcano decimated the southern 23rds of the island. Monitoring,evacuation,public information and exclusion zones were used to minimise the risk to the public. The only deaths were caused by islanders flouting the danger zone restrictions and being caught up in a pyroclastic flow.The islands capital town,Plymouth,the airport and numerous houses and farms were destoyed by pyroclastic flows and could not be returned to. Montserrat is governed by the the UK so although so had the help of a wealthy nation to rebuild. A whole new infrastructure had to built to accomodate the population on the island. The map shows the hazard zoning on the island.
Mount Unzen 1991Mount Unzen in Japan had been dormant for nearly 200 years when increasingly frequent earthquakes,small steam and ash eruptions heralded the start of an active phase. A lava dome appeared in May 1991 and began producing pyroclastic flows. The governemnt issued an evacuation order and definded a restricted zone. The eruption increased in intensity and 12000 people were evacuated in June. Pyroclastic flows reached Shimabara City and destoyed empty homes. During March 1992 there 500 pyroclastic flows. Eventually the eruption clamed down in 1995 , the civilian population had been protected but 43 people from the media and sciencs had been killed when they knowingly went into the danger zone.
Volcanic Hazard Control
Lava Diversion on Etna
In 1991-1993 a lava flow from Mt Etna threatened the town of Zafferana .Efforts were made to divert the lava flow away from the town. First earth barriers were constructed but were overcome. Explosives were then used to disrupt a 7km long lava tube system which was feeding the lava front. On 23 May an explosion was set off which destroyed the lava tube and diverted the channel into a manmade channel. Ironicaly the eruption quietened down- but the town was safe.
Eldfell is a cinder cone 200m high on the island of Heimay in the Vestmann islands off the south west cost of Iceland. At 1.55am on the 23 january 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.