Natural disaster

DISASTER CAUSED BY RABBITS 1. Is it possible for rabbits to cause a natural disaster? Yes, if they occur in extreme numbers. In Australia in the 1950s rabbits, with few natural enemies, had multiplied dramatically. They are herbivores (they eat plants) and in some areas had picked the land so bare that erosion set in and the land could no longer be farmed. 2. How did the Australians deal with the rabbit plague? The government put up thousands of miles of wire fences but the rabbits burrowed beneath them to find their food. Farmers tried poisons but other animals found the poison too. Foxes were introduced but they preferred lambs and chickens which were easier to catch than the rabbits. Finally, in yet another attempt to reduce the numbers of rabbits they were intentionally infected with an experimental virus. 3. What was the most successful effort to deal with this plague? The virus infection. In 1950 Australian scientists infected some rabbits with a virus that had, for many years, been known to cause disease in rabbits and had been tested in Brazil in the late 1940s. They released the infected rabbits into the areas where the worst rabbit infestions existed. The virus, myxoma, was transmitted from rabbit to rabbit by mosquitos and rabbit fleas. Over the next three years rabbits died of myxomatosis by the millions, grass grew back on the pastures, and sheep farming began to flourish again.

Rabbits

4. What else happened as a result of the introduction of Myxoma to the rabbit population?

There was a sudden upset in the balance of nature. The Myxoma virus had been successfully introduced into European rabbits too and, especially in England, with a scarcity of rabbits, foxes began eating poultry, rats and mice. The resulting reduction in the numbers of mice caused a decline in the numbers of owls whose normal diet (mice) became less abundant - and the upset continued on down the food chain. Scientists believe that, as populations of rabbits with resistance to Myxoma increase, there will be rabbit plague problems again. [Top of page]

DISASTER CAUSED BY INSECTS

5. Do insects ever cause natural disasters?

Yes. Locusts periodically cause natural disasters in several parts of the world. Locusts (order Orthoptera) are identical in appearance to grasshoppers but locusts can exist in two different behavioural states (solitary and gregarious) whereas grasshoppers do not. When the locust population density is low the locusts behave as individuals. However, when the population density increases locusts form highly mobile swarms.The change from solitary to gregarious is generally accompanied by changes in body shape and colour.

6. What causes the increase in locust populations? In Australia locust plagues occur when widespread inland areas receive good rainfall in successive seasons. High rainfall stimulates the growth of grass which creates an ideal habitat for locust breeding. The timing of the rainfall is important. When there are several wet seasons (winter, spring and summer) locusts can complete several generations in a single year. This results in overcrowding of developing nymphs (young insect stage) and stimulates the change to the gregarious, swarming phase. If wet seasons continue the swarming phase is prolonged. A series of dry seasons is necessary for the locust population numbers to decrease thus stimulating the change to the solitary form of the insect. 7. What sort of natural disaster is caused by swarming locusts? Locusts are vegetarians. As they swarm and migrate they devastate grasslands and crops in the areas they pass through. The results are similar to the disaster caused by the rabbit plagues in Australia. Once started, a locust plague is just about impossible to stop. Various efforts have included destroying egg masses laid by migrating swarms. Hopperdozers can also be used. These are large screens on wheels and are driven into a moving swarm so that the insects hit the screens and drop into troughs containing water and kerosene. 8. Where in the world do locust plagues occur? The migratory (swarming) locust is widely distributed around the world. It is found in grasslands in tropical Australia and New Zealand, Africa, Egypt, India, Iran, Italy, Palestine, Syria, Central and South America, and, in the 1870s, the Canadian Prairies.

Grasshopper (same family as the locust) [Top of page]

DISASTER CAUSED BY BACTERIA

9. Are natural disasters ever caused by micro-organisms?

Yes. Our world is teaming with micro-organisms (one-cell organisms that are too small to see). Most are innocuous, many are beneficial either to plants or animal life, but a few are harmful. The micro-organisms at issue here are bacteria and viruses. The natural disasters that can be caused by bacteria or viruses include such devastating events as the Black Death which killed about one third of the population of Europe in the fourteenth century, and AIDS sometimes seen as the modern Black Death even though its causative factor is different from that of the medieval disease.

10. What micro-organism caused the plague known as the "Black Death"?

The "Black Death" was caused by Yersinia pestis (also called Bacillus pestis and Pasteurella pestis) which is a bacterium. Yersinia pestis has almost certainly been causing plague epidemics in human populations for more than 2000 years. It was an outbreak of this plague in Europe in the 14th century that was called "The Black Death".

11. When was this plague bacterium identified? It was identified in 1894 by Alexandre Yersin. 12. What makes this bacterium so dangerous? The Versinia pestis bacillus (bacterium) is remarkably stable and vigorous. In humans it causes three phases of infection. The bubonic phase involves swelling of the lymph nodes, the pneumonic phase involves the lungs, and in the third, most serious phase called the septicemic phase, the blood stream is invaded and death occurs quickly. The disease can now be controlled and cured with the use of antibiotics. 13. How does a person become infected with this bacterium? The disease is most commonly passed to humans through bites from fleas that have fed on the domestic rat, Rattus rattus. This was not fully realized until 1914. Today the disease is not common but small outbreaks can still occur in crowded, unsanitary situations where the rat populations are not controlled. [Top of page]

Plague bacteria. Image copyright Dennis Kunkel

VIRUS DISASTER

14. What modern natural disaster is caused by a virus?

AIDS (Acquired Immune Deficiency Syndrome) is caused by a virus which is currently (20th and 21st centuries) causing a modern natural disaster sometimes described as the modern Black Death. The AIDS virus is the Human Immunodeficiency Virus (HIV) and while there is no certain cure yet for AIDS, infection by the HIV does not always result in a case of AIDS.

15. Is a virus different from a bacterium? Yes. Bacteria are living, single-celled organisms. Viruses are much smaller than bacteria and are not living organisms in the generally accepted sense. Viruses are collections of protein molecules without the cell membrane, protoplasm, nucleus etc. normally considered to be part of the cell of a living organism. When a virus invades living tissue it is able to replicate itself and to affect its host in ways that are recognized as illness or disease. Outside its living host a virus is completely inert. Viruses invade all types of living organisms (plants as well as animals). Not all viruses cause disease but many do. Viruses are not affected by antibiotics. 16. What diseases are caused by viruses?. In addition to the very serious AIDS, viruses cause the more common, and less severe, common cold and warts as well as the extremely serious rabies, and some types of cancer. Of the several families (types) of viruses: papoviruses cause warts; adenoviruses cause respiratory and eye infections; herpesviruses cause cold sores, chickenpox, and shingles; orthomyxoviruses cause influenza; coronaviruses cause the common cold; and retroviruses cause AIDS.

AIDS virus [Top of page]

NATURAL FIRE

17. Fires can be disastrous. Do fires ever start without human intervention?

Yes. Fires can be initiated in many ways and the results, when controlled are can be beneficial but uncontrolled fires can be disastrous whether they are natural or man-made.

18. What is fire? Scientists, who use the term "combustion" instead of "fire", explain the phenomenon as a chemical reaction in which a combustible substance reacts rapidly with oxygen. The chemical reaction may need heat to get it started. For example, when striking a match, the friction provides sufficient heat to cause the chemicals in the match head to react. Energy stored in the match-head is released as heat energy which ignites the wood of the match stick. So long as sufficient heat energy continues to be available the wood of the match stick reacts with oxygen in the air in such a way that the substance of the wood is changed to ash and gases. Flames associated with combustion are a gaseous mixture of incandescent small particles often of carbon, and rapidly moving and fluorescing molecules and ions. The smoke associated with fire is comprised of cooling gases and small ash particles. 19. What are typical causes of naturally occurring fires? By naturally occurring fires we mean ones that are not 'man-made'. About 90 percent of wildfires are started by humans. The other 10 percent are started by lightning The necessary ingredients for combustion - a combustible substance, oxygen, and heat - are often present in situations where natural phenomena such as lightning, hot volcanic lava, or friction, are capable of intiating combustion. Lightning and hot lava are intrinsically hot enough to start fires. Friction produces heat that in some cases can be sufficient to start a fire. Biological activity can sometimes create enough heat to start a fire as, for example, in a damp haystack where microorganisms growing and reproducing can produce sufficient heat to set the haystack burning. 20. What are some specific examples of natural-fire disasters? Caused by the April 18, 1906 San Andreas Fault earthquake, a fire in San Francisco destroyed 28,000 buildings in 500 city blocks. The earthquake was a natural force and human action was not responsible for the fire. However, the fire only happened because of the presence of humans and their dwellings. Caused by lightning, a disastrous fire in 1910 swept across three million acres of Idaho for several weeks. Caused by an earthquake, a ferocious fire in 1923 destroyed more than half of Japan. [Top of page]