Chapter 3 ACTIVITYS Natural Hazards In Australia 3.1 Natural hazards and natural disasters: 1. What is the difference between a natural hazard and a natural disaster? A hazard is an event or object that is a potential source of harm to a community. A disaster occurs as the result of a hazardous event that dramatically affects a community. 2. Explain how a bushfire can be both a natural and human hazard. A bushfire can be caused by careless humans, we also impact them by inadequate preparation and poor disaster planning 3.2 Droughts: 1. What is meant by the term ‘drought’? A prolonged period of abnormally low rainfall, resulting in a shortage of water. 2. What is the difference between drought and low rainfall? A drought happens when there is not enough water for a community’s needs, therefore if it was a small town with low rainfall it may not be a drought where as if it was Sydney with low rainfall its more likely to be a drought. 3. Explain why there is little chance that all of Australia would be affected by drought at the same time. Rainfall is common in some places more than others, also some towns are large and require a higher amount of rainfall then a smaller town. 4. How often might droughts be expected to occur in Australia? Between 4 and 38 years. 5. What are the two main types of drought that occur in Australia in terms of duration? Short and intense or long lived 6. Describe the economic impacts of a drought in Australia. The drought of 1963–68 affected large parts of the continent and was the longest drought ever in central Australia. The last two years of the drought saw a 40% decrease in the wheat harvest, the loss of 20 million sheep and a decrease in farm income of around $500 million. 7. Why does Sydney store more water than any other comparable size city in the world? Because Australia is one of the driest countries in the world and has to be prepared for common droughts and low rainfall 3.5 Bushfires: 1. What is a bushfire? A fire in the bush, scrub or forest that spreads rapidly. 2. How have bushfires been an essential input into some Australian ecosystems? Ash left over from bushfires is rich in potassium, calcium and magnesium, which help return minerals to the soil, making the ground more fertile. Also the heat from the fire releases seeds to begin new growth. 3. What is arson? How could arson be the cause of some of the worst bushfires? Arson is the deliberate setting of fires and can cause some of the worst bushfires because stupid people can start it with stronger fuels over bigger areas. 4. How could very strong, hot winds affect crown fires and make them very dangerous? Hot winds as well as dry vegetation make bushfires spread rapidly 3.9 Storms: 1. Explain what is meant by (a) a storm, (b) a thunderstorm and (c) a severe thunderstorm. a. A storm: a violent disturbance of the atmosphere with strong winds and usually rain, thunder, lightning, or snow. b. A thunderstorm: a storm with thunder and lightning and typically also rain. Occurs with cumulonimbus clouds. c. A severe thunderstorm: a thunderstorm featuring one or some of the following; hail stones, wind gusts, tornados, heavy rain. 3.11 Tropical cyclones: 1. What is a tropical cyclone? A system of winds rotating inward to an area of low atmospheric pressure, with a counterclockwise (northern hemisphere) or clockwise (southern hemisphere) circulation 2. Why do tropical cyclones usually die out if they move inland? Because the warm water vapor from the ocean helps the cyclone form 3.12 Floods: 1. Define a flood and describe the three main types of floods. An overflowing of a large amount of water beyond its normal confines, especially over what is normally dry land. 1. Slow-onset floods. These occur along the flood plains of inland rivers and may last for weeks and even months. They are caused by heavy rain and run-off upstream, and the water can take days and even weeks to affect farms and towns downstream. 2.Rapid-onset floods. These occur in mountain headwater areas of larger inland rivers or rivers flowing to the coast. The rivers are steeper and the water flows more rapidly. Rapid-onset floods are often more damaging because there is less time to prepare. 3. Flash floods. These occur due to heavy rainfall of short duration, such as in a severe thunder- storm. This type of flooding causes the greatest risk of property damage and loss of life as it can happen so quickly. It can be a serious problem in urban areas where drainage systems are inadequate. 3.13 Earthquakes: 1. What are the focus and the epicenter of an earthquake? A focus is the area underground where the Earth’s crust has snapped, sending shock waves to the surface. The point on the Earth’s surface above the focus is called the epicenter. 2. How are earthquakes measured? On a seismograph 3. What does the Richter scale measure? The amount of energy an earthquake releases 4. How much greater is the magnitude of an earthquake of 8.0 than one of 7.0? 8.0 is 30 times greater than 7.0 5. Describe the damage caused by earthquakes with the following measurements on a Modified Mercalli scale: a. II: not felt by people generally. Just recorded by a seismograph. b. V: things indoors fall over. c. VI: houses suffer considerable damage, some collapse. d. IX–X.: houses collapse everywhere, complete destruction.