Volcanoes can pose many hazards but not only in the immediate vicinity of an eruption. Volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere.
A volcano forms when a break in the earth’s crust allows magma and hot gas to reach the surface. The magma and hot gases are under extreme pressure, resulting in dangerous eruptions.
Volcanoes come in all different shapes and sizes. Some volcanoes have very steep sides that have been caused by the piling up of volcanic material over time, whilst others have shallow slopes from very runny lava.
Volcanoes can also look like depressions in the ground which are caused when the land sinks from explosions under the ground.
There are over 1,500 potentially active volcanoes worldwide and eight to ten can be erupting at one time. There are also many more dormant and under ocean volcanoes around the world.
Types of volcanoes
There are many types of volcanoes, but here are five major types:
Caldera – a large depression in the earth that is created when a volcano collapses.
Cinder Cone – a volcano that is built from blobs of lava that are ejected from a single vent.
Shield Volcano – a volcano that builds up from countless outflows of fluid lava.
Stratovolcano – volcanoes that are made up of layers of ash, lava and volcanic debris.
Lava Dome – large mounds that form from lava that piles up around a vent.
Although the vast majority of volcanoes in Australia are extinct, scientists believe further minor volcanic activity is possible from long dormant ones in South Australia and Victoria.
There are two active volcanoes in the Australian Antarctic Territories of Heard Island and McDonald Island. The bigger of these two volcanoes is called Big Ben (2750 m). The volcano on McDonald Island is an active volcano, having erupted for the first time in 1992 and again in August 2005.
The Ring of Fire
The image below shows that about 80 per cent of the world’s volcanoes form a circle around the Pacific Ocean in a belt known as the 'Ring of Fire'.
In the Australian region, the ‘Ring of Fire’ volcanoes in Indonesia and the Philippines have erupted as recently as 1982 when the Galunggung volcano in West Java caused the engines of a passenger plane to stop as it was flying towards Australia.
In 1991, Mt Pinatubo in the Philippines erupted threatening the lives of a million people. A giant ash cloud rose 35 km into the sky. The Philippine authorities were able to evacuate 60,000 people from the slopes and valleys, and the American military evacuated 18,000 people from a nearby base.
Our closest neighbours
In Papua New Guinea, two volcanoes, Vulcan and Tavurvur, erupted and literally buried the town of Rabaul under millions of tonnes of ash, resulting in 80,000 people becoming homeless.
In New Zealand, Mt Ruapehu erupted in late 1995 and again in June 1996, closing ski fields, causing floods from its crater lake and interrupting air traffic in the North Island.