Hazard fact – 26 August 2005 Volcanoes can cool climate Powerful volcanic eruptions in which large amounts of volcanic ash and gases are blasted into the upper levels of Earth’s atmosphere can cool the world’s climate for several years after the eruption. Although volcanic ash settles out of the air in a short time, volcanic gases such as sulphur dioxide can form sulphuric acid particles that reflect solar radiation, preventing it from reaching the Earth’s surface. For example, the eruption of Mount Pinatubo in the Philippines in 1991 cooled global average temperatures by up to 1.5 degrees C. 11:26 AM
19.8.05
Raising mountains During the movements of the Earth’s crust that cause earthquakes, large areas of land may move up, down or sideways. In the Wellington region, during a magnitude 8.2 earthquake in 1855, the southern end of the Rimutaka Range was raised by up to 6 metres! 11:23 AM
12.8.05
A City of Volcanoes Auckland is built on a volcanic field, with many square kilometres of lava flows and over 45 volcanic vents and cones. Most of the city’s hills - for example One Tree Hill, Mount Eden and Mount Albert - are small volcanic cones. The most recent eruption was on Rangitoto Island about 600 years ago. 1:42 PM
5.8.05
Earthquake magnitude Earthquake magnitude is a measure of the size of an earthquake at its source. Each increase in the magnitude number by one represents the release of about 32 times more energy. Thus a magnitude 6 earthquake releases about 32 times more energy than a magnitude 5, and a magnitude 7 earthquake releases about 1,000 times more energy than a magnitude 5. 1:40 PM
