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Part 2: Optional Themes – Option D – Hazards and Disasters Characteristics of Hazards


Subject requirements: Characteristics: ∗ Explain the characteristics and spatial distribution of the following hazards. ∗ Either earthquakes or volcanoes ∗ Hurricanes (tropical cyclones, typhoons) ∗ Droughts ∗ Any one recent human-induced (technological) hazard (explosion or escape of hazardous material) ∗ Distinguish between the chosen hazards in terms of their spatial extent, predictability, frequency, magnitude, duration, speed of onset and effects.


Characteristics of Hazards Magnitude: ∗ The size of the event, e.g. Force 10 on the Beaufort scale, the maximum height or discharge of a flood, or the size of an earthquake on the Richter Scale. Frequency: ∗ How often an event of a certain size occurs e.g. a 1 meter high flood could occur on a river once a year on average. However, a 2 meter flood maybe once every 10 years. The frequency is sometimes called the recurrence interval (Gumbel's Laws). The larger the event, the less frequently it occurs. So for earthquakes, magnitude 8 or more events are less frequent than magnitude 3 or 4 events but much more devastating.


Continued….. Duration: ∗ The length of time that an environmental hazard exits. This varies from a matter of hours, such as with urban smog, to decades, in the case of drought, for example Areal extent: ∗ The size of the area covered by the hazard. This can range from very small scale, such as an avalanche chute, to continental, as in the case of drought. Spatial concentration: ∗ The distribution of hazards over space; whether they are concentrated in certain areas, such as tectonic plate boundaries, coastal locations, valleys and so on.


And more….. Speed of onset: ∗ The time difference between the start of the event and the peak of the event. It varies from rapid events, such as the Kobe earthquake, to slow time-scale events such as drought in the Sahel of Africa. Regularity (or temporal spacing): ∗ Some hazards, such as cyclones, are regular; whereas others, such as earthquakes and volcanoes, are much more random.


Earthquakes Let’s watch the video: ∗ Consider - location, prediction, frequency and magnitude?


Task one: Spatial extent ∗ Describe the global distribution of earthquakes with a magnitude greater than 2.5 that have occurred in the last 7 days? (You could get an exam question like this based upon a given map!) ∗ Look at the global distribution of earthquakes with a magnitude 8 or greater that have occurred since 1900. Is there any difference between the observed distribution and the distribution of earthquakes with a magnitude greater than 2.5 that have occurred in the last 7 days? ∗ So what is determining the location of global earthquakes?


Characteristics of hazards