Answering questions
Marjorie Henry, Contributor

The discussion of question eight from the June 2008 paper started in the previous lessons. In completing section (b) of that question, I will now turn your attention to the possible ways in which volcanic eruptions and hurricanes have affected life or property. Remember that in your answer you must refer to a country you have studied. I will begin with volcanic eruptions.

Ways in which volcanic eruptions have affected life or property include:

1. Lava flows - Lava is hot, molten rock which may flow to the surface from a volcano. Lava flows are a threat, but they are usually slow enough that people can get out of the way. Economic loss from lava flows is common. They destroy everything in their paths - houses, roads, vegetation.

2. Falling ash - In an explosive eruption, pent-up gases escape violently. Magma breaks into pieces and bursts from the volcano in a column of ash and fiery fragments. The cooled fragments that fall back to Earth are called tephra. In a large eruption, tephra can cover vast areas with a thick layer of ash, presenting a much greater hazard than lava flows. Large fragments of tephra can cause significant damage on impact, colliding with structures or setting things on fire. Accumulations of tephra do their damage by burial: roofs collapse, for example, or crops are killed.

3. Pyroclastic flows - These are mixtures of very hot gas and tephra that cascade down a volcano's sides at high speeds. They cause damage by burial and incineration and, because of their speed and gas content, can cause impact damage and asphyxiation.

4. Mud and debris flows - Debris flows, fragments of mud and other debris that flow down the sides of a volcano, are another serious and little-known hazard. Debris flows often form when part of the volcano collapses, breaks up and flows downhill. If the collapse is a major one, the large flow that results can travel great distances, often burying everything in its path. These are particularly dangerous on volcanoes that have glaciers on top, as the eruption instantly melts the ice, causing a massive mud slide.

5. Eruptions can also cause tsunamis, volcanic earthquakes or the release of suffocating gases. These hazards pose serious threats to both life and property.

Ways in which hurricanes affect life or property

1. Hurricane winds are high-velocity winds over 120 km/h and, therefore, have great physical strength. Here are some of the damage that result from these strong winds:

• taking off of roofs
• damaging crops such as bananas
• blowing down trees which, in turn, can crush buildings or block roads
• toppling of utility poles, hence disrupting the supply of these services
• flying debris, such as sheets of roofing material, may kill or injure people and cause further damage to buildings
• carrying of people into the air
• demolishing of walls, particularly those in a state of disrepair or with no reinforcing steel bars.

2. Waves may reach eight metres high and can cause:

• severe beach erosion
• marine life to be damaged and coral broken and killed
• coastal structures to be torn down
• ships and boats to be at risk, whether they are in sheltered harbour or out at sea.

3. Storm surges may flood coastal areas.

4. Hurricanes bring heavy rain over a wide area. These torrential rains can result in the flooding of valleys. As the water rushes down the valley, it may knock down buildings, wash away vehicles or drown those in its path. On flat land, wide areas can be flooded by slowly rising waters. Furniture may be ruined, vehicles damaged and crops destroyed. Floodwater also threatens disease, by spreading sewage and animal waste into the drinking water.

5. Landslides are triggered where steep hillsides are sodden after heavy rain, which increases the weight of the soil and rock, and lubricates the soil and rock particles so that they can move more easily. Landslides may push down and bury houses and block roads.

The discussion on this question continues in the next lesson.

Preparations for the upcoming Caribbean Secondary Education Certificate examinations is ongoing for these Anchovy High School students during this mathematics session. - photo by Sheena Gayle