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S5 Geography | Natural Hazards Paper 2 (Advanced)
S5 Geography | Natural Hazards Paper 2 (Advanced)
Paper 2 handles frequency and risk: fractional magnitude differences, wind speed squared, return periods and exceedance, slope factors of safety, reservoir days and soil amplification.
Attempt first, mark afterwards Allow about thirty minutes; write probabilities as one minus (one minus p) to the power n, separate total cost from cost per metre per year, and remember a factor of safety below one means failure.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 items |
| Suggested time | About 30 minutes |
| Difficulty mix | Foundation 3 · Intermediate 4 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S5 Geography | Natural Hazards |
| Level | S5 (Secondary 5) Geography |
02 Questions (10 items)
- FoundationOne earthquake measures 6.2 and another 7.2. How many times more energy does the larger release?
- FoundationCyclone A has winds of 130 km/h and B has 210 km/h. Dynamic pressure goes as the square of speed, so how many times greater is B?
- FoundationA pyroclastic flow races down a valley at 100 km/h toward a town 12 km away. How many minutes does it take?
- IntermediateA flood has a return period of 50 years. What is the chance in any one year, and the chance of at least one in the next ten years?
- IntermediateA slip surface has shear strength 45 kPa and dry-season shear stress 30 kPa. What is the factor of safety, and what does it become when storm water raises the stress to 40 kPa?
- IntermediateFlood water stands 1.5 m deep over a floodplain 800 m wide and 5,000 m long. What volume is stored?
- IntermediateA reservoir holds 30,000,000 cubic metres in total but is only sixty per cent full in the dry season, while the city uses 250,000 cubic metres a day. How many days of supply remain?
- ChallengeSoft soil amplifies ground shaking 3 times and a 2.5 storey building resonates for another 2.5 times. What is the combined amplification, and the roof amplitude if bedrock shaking is 0.05 m?
- ChallengeA tsunami reaches water 20 m deep, where speed is about the square root of 9.8 times depth. What is the speed in m/s and km/h, and how many seconds of warning for people 3,000 m inland?
- Error redoA student says a one in a hundred year flood happens exactly once every hundred years, so moving in this year is safe. What is wrong, and what is the chance of at least one flood in thirty years?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | About 31.62 times. | Ten to the power 1.5 times 1 is 31.62, which handles fractional magnitude differences directly. |
| 2 | About 2.61 times. | 210 divided by 130 is 1.62, and squaring gives 2.61; a sixty per cent faster wind more than doubles the pressure. |
| 3 | 7.2 minutes. | 12 divided by 100 is 0.12 of an hour, or 7.2 minutes; pyroclastic flows outrun lava and kill far more people. |
| 4 | 2 per cent a year, and about 18.29 per cent over ten years. | One over 50 is 2 per cent, and the ten-year chance is one minus 0.98 to the tenth, or 18.29 per cent; you cannot simply multiply by ten. |
| 5 | 1.5 when dry and 1.12 after rain. | 45 divided by 30 is 1.5, and by 40 is 1.12; below one the slope fails, so 1.12 is dangerously close. |
| 6 | 6,000,000 cubic metres. | 1.5 times 800 times 5,000 is 6,000,000 cubic metres, assuming a mean depth that in reality tapers away from the levee. |
| 7 | 72 days. | Sixty per cent of 30,000,000 is 18,000,000 cubic metres, which at 250,000 a day lasts 72 days; drought risk uses usable storage, not headline capacity. |
| 8 | A total of 7.5 times, giving about 0.38 m at roof level. | 3 times 2.5 is 7.5, so 0.05 m becomes 0.38 m; amplifications multiply, and resonance is worst when building and ground periods match. |
| 9 | 14 m/s, or 50.4 km/h, giving about 214 seconds. | The square root of 9.8 times 20 is 14 m/s, and 3,000 m at that speed takes 214 s, so evacuation must be rehearsed in advance. |
| 10 | It is about one per cent a year and not periodic, so the thirty-year chance is about 26.03 per cent. | A return period is a long-run average frequency, identical every year, and one minus 0.99 to the thirtieth is 26.03 per cent; assuming safety because a flood just happened is the gambler fallacy. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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