A volcano is a mountain opening downwards to the reservoir of molten rock towards the surface of earth. Volcanoes are made by the accrual of igneous products. As the pressure from gases in the molted rock becomes intense, the eruption takes place. The volcanic eruption can be either quiet or volatile. Its aftermaths include flowing lava, flat landscapes, poisonous gases and fleeing ashes and rocks. The secondary disaster after the eruption such as debris flows are often triggered by rainfall after the volcanic eruption.
- Shield volcano
When magma is very hot and runny, gases can escape and eruptions are gentle with considerable amounts of magma reaching the surface to form lava flows. Shield volcanoes have a broad, flattened dome-like shape created by layers of runny lava flowing over its surface and cooling. Because the lava flows easily, it can move down gradual slopes over great distances from the volcanic vents.
- Composite volcano
Also known as strato-volcanoes, these volcanoes are characterized by an explosive eruption style. When magma is slightly cooler it is thick and sticky, or viscous, which makes it harder for gas bubbles to expand and escape. The resulting pressure causes the magma to foam and explode violently, blasting it into tiny pieces known as volcanic ash. These eruptions create steep sided cones.
- Caldera volcano
These erupt so explosively that little material builds up near the vent. Eruptions partly or entirely empty the underlying magma chamber which leaves the region around the vent unsupported, causing it to sink or collapse under its own weight. The resulting basin-shaped depression is roughly circular and is usually several kilometers or more in diameter. Although caldera volcanoes are rare, they are the most dangerous. Volcanic hazards from this type of eruption include widespread ash fall, large pyroclastic surges and tsunami from caldera collapse.
We can classify the impacts of volcano into direct and indirect impact. Direct impacts are:
- Mediated trauma, crush type injuries, and lacerations can be caused by explosion and contact with volcanic mass.
- Hot ash, gases, rock and magma cause skin and lung burns, asphyxiation, conjunctivitis or corneal abrasion.
- Breathing the gases and fumes can cause acute respiratory distress.
- Acid rain provokes eyes and skin irritation.
In the case of ash fall, particularly in fine particles, bronchial asthma and other chronic respiratory conditions can be aggravated in children as well as in adults. Death is highly improbable. Nonetheless, it can occur in persons with serious symptoms if they do not protect themselves from the ashes.
Ashes can have toxic consequences (i.e. gastrointestinal problem) due to ingestion of contaminated food or water.
- Ashes can have mechanical consequences. The weight of ash may cause collapse of building (i.e. trauma).
- Damage on health infrastructures and water systems can be severe. Problem of communication (ashes create serious interference) and transportation (poor visibility and slippery roads) are likely to happen.
There are several steps in emergency situation to respond a volcanic eruption.
Before the eruption:
- Demarcation and evacuation of areas of risk.
- Formulation of and familiarization with search and rescue plans.
- Preparation of hospital emergency plans to cope with large influx of patients with burns, lung damage and trauma.
- Identification of facilities to collect and analyze ash for toxic elements and drinking water quality.
- Facilities and equipment for monitoring air.
- Plans for procurement of emergency supplies.
- Report any and all unusual physical changes around volcanoes to the Seismic Research Unit, e.g. the drying up of vegetation, rumbling sounds, earthquakes, landslides and other possible abnormalities.
During the Eruption:
- Pay attention to Warnings, which would include evacuation notices and escape from area as quickly as possible.
- Listen to the radio for information and advice.
- Find shelter, but NOT in a building with low-pitched or flat roof, if heavy ash is falling.
- Avoid basements and closed spaces where gases may accumulate.
- Wear protective clothing over head and body if you have to move in an ash shower.
- Breathe through a handkerchief.
- Always carry a flashlight, even during the daytime.
Volcanic mitigation can be maintained into structural and nonstructural measures. In structural measures, various facilities are installed to minimized damage by volcanic mudflow, pyroclastic flow and lave flow as well as sediment-related disaster caused by rainfall. To establish the nonstructural measures such as a warning and evacuation system in parallel with structural measure is also an important way. Some preparations that can be made such as hazard maps, monitoring camera, establishment of permanent danger zone, educate people about volcano risks, improving warning and evacuation system, etc.
See also an example of volcanic risk mitigation plan in New Zealand.
Several actions related to volcano management plans.
2. Contingency plan for the Auckland volcanic field (click here)
3. Mount St. Helens volcanic activity response plan. (click here)