An essay on Natural Hazard; Storms and Black Saturday, Canberra, 2003

Essay by BYLuoHigh School, 10th gradeA+, July 2008

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On 18 January 2003, Canberra was hit by the mostdevastating bushfire in its history. Canberra'sfirestorm had its beginnings on 8 January, whenlightning strikes in adjacent national parksignited a number of bushfires. Shifting windswidened the fire fronts of these fires, joining sometogether. Eight days later, strong south-westerlywinds drove the bushfire towards the nationalcapital.

The fierce winds blew burning embers ahead ofthe fire front, igniting spot fires in and aroundhouses on the capital's south-western edge. Attimes, the shower of embers blew horizontally.

There was little the 500 firefighters and 100police could do to stop such a massive blaze.

Their work was made more difficult by thebillowing black smoke (which reduced visibility),by power and water-pressure failures, and by therapid spread of the fires.

The conditions in and around Canberra on 18 Januarywere perfect for a firestorm. There was ahuge supply of fuel. (Canberra is sometimes calledthe `bush capital', as it is virtually surrounded bybushland and pine plantations and has a numberof bush/pine corridors.)

This fuel was tinder drydue to the prolonged drought. On the day of thefire, very high temperatures, strong winds andextremely low relative humidity turned theadvancing bushfire into a fireball.

The firestorm destroyed 530 homes Ð somein little more than 10 minutes Ð and about30 farms. Four people lost their lives, as didhundreds of cattle, thousands of sheep andmany thousands of native animals. About12 million trees were destroyed by the ®re.

Powerlines exploded and the famous MountStromlo Observatory was burnt down. Aswell as destroying lives, homes and livelihoods,the damage bill was expected to top$280 million.

What is a storm?A storm is any violent disturbance of the atmosphereand the effects associated with it. Themain types of storms are thunderstorms, tropicalcyclones, cold fronts and tornadoes (twisters). Inthis section, we look at thunderstorms and theireffect on people's activities.

A thunderstorm is a storm associated with lightningand thunder and occurs with cumulonimbusclouds. Cumulonimbus clouds can occursingly or extend over an area of 100 kilometresor more. Thunderstorms occur when cumulonimbusclouds build up enough static electricityto produce lightning. Lightning instantly heatsthe air through which it travels to about 20 000°Celsius Ð more than three times as hot as thesurface of the sun. This causes the air to expandso quickly that it causes an explosion (thunder).

ningand thunder and occurs with cumulonimbusclouds. Cumulonimbus clouds can occursingly or extend over an area of 100 kilometresor more. Thunderstorms occur when cumulonimbusclouds build up enough static electricityto produce lightning. Lightning instantly heatsthe air through which it travels to about 20 000°Celsius Ð more than three times as hot as thesurface of the sun. This causes the air to expandso quickly that it causes an explosion (thunder).

Severe thunderstorms can be a serious naturalhazard because they can bring one or more of thefollowing features:· Hailstones, which are two centimetres or morein diameter· Wind gusts of 90 kilometres or more per hour· Tornadoes, which are rapidly rotating columnsof air that descend in a funnel-shape fromthunderstorm clouds· Very heavy rain, which can result in ¯ash¯ooding. A thunderstorm often moves slowly,dropping a lot of precipitation in one area. Therain or hail may be too heavy and prolongedfor the ground to absorb the moisture. Thewater runs off, quickly ¯ooding local areas.

http://members.pcug.org.au/~mdinn/fires/index.htmhttp://www.rmwebed.com.au/geo_2008/canberra.htmlhttp://members.pcug.org.au/~mdinn/fires/index.htmhttp://www.rmwebed.com.au/geo_2008/canberra.html