Class: 9A

Teacher: Mr Chapman

Task: Natural Hazards ICT WebPage

An ordinary thunderstorm is generated when warm, humid air at ground levels rise rapidly in unstable conditions (generally low pressure systems). As more warm air rises, they condense to form cumulous clouds, which will grow and expand. These clouds will then produce tiny water vapors which form larger droplets.

Eventually the quantity of water droplets produced will become too heavy for the rising air to support. Also, cool air will join the cumulous clouds, but stay towards the lower sections of the clouds, because cold air is heavier than warm air. The heavier cool air as well as the forces of gravity drag the water droplets downwards and results in rain.

Now depending on the surrounding conditions, the thunderstorm will produce different results.

• Hail is formed when the water vapors freeze to become a solid, falling to the ground in the same manner as ordinary rain.
• Wind Gusts are started when the falling rain and hails drag the surrounding atmospheric air downwards as they drop to the ground. Also, as these rain and hail fall, they may also evaporate which cools nearby air and accelerates the downward rush. These forces hit the ground and then spread out laterally across the land, producing strong windy conditions which can sometimes cause major damage.
• Flash floods are basically the result of a lot of rain affecting a concentrated area. These are started if there is enough water droplets formed in clouds to be released as an ongoing downpour of rain. The movement speed of the thunderstorm and the rain clouds can also determine the possibility of flash floods. Generally if the storm moves slowly, a single area receives the majority of the rainfall since the clouds do not move quick enough to disperse the rain droplets elsewhere. This allows a concentrated area to be affected with the immense rainfall, causing flash floods.
• Tornadoes are quite rare and are formed when air rotates extremely quickly in a column formation underneath the base of a storm cloud. Most tornadoes are known to form in a funnel shape which rotates and moves along the ground, sucking objects in its path into the massive tube of air.

The severity of the thunderstorm varies depending on the surrounding conditions. Obviously larger, more destructive storms require greater energy and force to get them started, and vice versa.

Thunderstorms may become very severe and destructive if the atmosphere was to suddenly change into a more unstable condition and/or if additional energy is supplied and drawn from the surroundings (eg. Additional winds).

Click on the links below to find out more on:

• Page 2- Maps describing the areas of Australia most seriously affected

• Page 3-The impacts of the hazard on the environment, economy and people

• Page 4- The responses of society