The Saffir-Simpson scale rates hurricanes on the basis of what?

The overall diameter of the storm

The moment magnitude scale, now standard for large earthquakes, is calculated from what?

The total energy released, derived from the fault area and how far it slipped

The largest single wiggle recorded on one seismogram

The number of buildings reported damaged

The depth at which the rupture began

How does the Modified Mercalli scale differ from a magnitude scale?

It records the shaking and damage experienced at a particular place rather than the size of the quake

It applies only to earthquakes occurring beneath the sea

It is read from instruments rather than reported by observers

It runs from 1 to 5 rather than from 1 to 12

The Volcanic Explosivity Index is based chiefly on what?

The volume of material erupted and the height of the eruption column

The temperature of the lava at the vent

How many days the eruption continues

The chemical composition of the magma

The Beaufort scale was originally devised to describe what?

The effect of wind on a ship's sails and on the state of the sea

The intensity of rainfall observed at sea

Wave height inside coastal harbours

A "hundred-year flood" is best understood as what?

A flood with roughly a one percent chance of being matched in any given year

A flood that occurs exactly once every century

The largest flood recorded in the past hundred years

A flood whose waters remain in place for a hundred days

The Palmer Drought Severity Index combines rainfall with which other factor?

Temperature, as a way of estimating how much moisture is lost to evaporation

Wind speed measured at ground level

River flow recorded at gauging stations

Crop yields from the preceding season

Deep-ocean tsunami detection buoys work by measuring what?

Very small changes in water pressure on the sea floor as the wave passes overhead

The surface temperature of the water above them

Ground motion recorded on the nearest coastline

The height of waves breaking against the buoy

In a hurricane forecast, what does the "cone of uncertainty" show?

The likely range of positions of the storm's centre, not the extent of its effects

The area that is certain to be struck

The region expected to receive the heaviest rainfall

The zone where the eye will be visible from the ground

In severe weather alerts, what does a "watch" mean as opposed to a "warning"?

Conditions are favourable for the event, whereas a warning means it is happening or imminent

A watch is issued at night and a warning during the day

A watch covers a smaller area than a warning

A watch applies to rainfall and a warning to wind

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Natural Disasters Medium ⚡ 10 Questions ⏱️ ~6 Mins +100 XP

How Disasters Are Measured

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Every hazard has a number attached to it, and most of those numbers mean something narrower than they appear to.

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About this topic

Hazard scales exist to compress a chaotic event into a figure that can be compared, communicated and planned around. They do that job unevenly. A hurricane category describes sustained wind and nothing else, which is awkward given that surge and flooding kill most of the people. A hundred-year flood is a probability, not a schedule, and two can arrive in consecutive years without anything being wrong with the statistics. A further split runs through the whole subject: some scales measure the event and some measure the experience. An earthquake has one magnitude but a different intensity at every location, which is why historic earthquakes can be rated from written accounts long before instruments existed. The questions here cover the main scales in use for wind, shaking, eruption, drought and flood, and the difference between a watch and a warning.

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How Disasters Are Measured: all 10 questions and answers

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1The Saffir-Simpson scale rates hurricanes on the basis of what?
- A Central pressure alone
- B Total rainfall delivered
- C The overall diameter of the storm
- D Sustained wind speed Correct
Answer: D. Sustained wind speed

Why: It runs from category 1 to category 5 and says nothing at all about storm surge or inland flooding, which cause the majority of hurricane deaths.
2The moment magnitude scale, now standard for large earthquakes, is calculated from what?
- A The number of buildings reported damaged
- B The depth at which the rupture began
- C The total energy released, derived from the fault area and how far it slipped Correct
- D The largest single wiggle recorded on one seismogram
Answer: C. The total energy released, derived from the fault area and how far it slipped

Why: It replaced the older Richter scale, which saturates at large sizes and cannot distinguish between the biggest events at all.
3How does the Modified Mercalli scale differ from a magnitude scale?
- A It runs from 1 to 5 rather than from 1 to 12
- B It records the shaking and damage experienced at a particular place rather than the size of the quake Correct
- C It applies only to earthquakes occurring beneath the sea
- D It is read from instruments rather than reported by observers
Answer: B. It records the shaking and damage experienced at a particular place rather than the size of the quake

Why: One earthquake has a single magnitude but many intensities, which is why old newspaper accounts can be used to rate events that predate seismographs.
4The Volcanic Explosivity Index is based chiefly on what?
- A The volume of material erupted and the height of the eruption column Correct
- B The temperature of the lava at the vent
- C How many days the eruption continues
- D The chemical composition of the magma
Answer: A. The volume of material erupted and the height of the eruption column

Why: Each step up the index represents roughly a tenfold increase in erupted volume, and the largest historically recorded eruptions sit at 7.
5The Beaufort scale was originally devised to describe what?
- A The intensity of rainfall observed at sea
- B Wave height inside coastal harbours
- C Visibility in fog and haze
- D The effect of wind on a ship's sails and on the state of the sea Correct
Answer: D. The effect of wind on a ship's sails and on the state of the sea

Why: A Royal Navy officer standardised it in 1805, long before instruments were common aboard ship, and specific wind speeds were fitted to the descriptions much later.
6A "hundred-year flood" is best understood as what?
- A The largest flood recorded in the past hundred years
- B A flood whose waters remain in place for a hundred days
- C A flood with roughly a one percent chance of being matched in any given year Correct
- D A flood that occurs exactly once every century
Answer: C. A flood with roughly a one percent chance of being matched in any given year

Why: Two can occur in consecutive years without contradicting the definition, and changes to river channels and land use shift the underlying figure over time.
7The Palmer Drought Severity Index combines rainfall with which other factor?
- A Crop yields from the preceding season
- B Temperature, as a way of estimating how much moisture is lost to evaporation Correct
- C Wind speed measured at ground level
- D River flow recorded at gauging stations
Answer: B. Temperature, as a way of estimating how much moisture is lost to evaporation

Why: Because evaporation increases with heat, a warm dry spell scores as more severe than a cool one with an identical rainfall shortfall.
8Deep-ocean tsunami detection buoys work by measuring what?
- A Very small changes in water pressure on the sea floor as the wave passes overhead Correct
- B The surface temperature of the water above them
- C Ground motion recorded on the nearest coastline
- D The height of waves breaking against the buoy
Answer: A. Very small changes in water pressure on the sea floor as the wave passes overhead

Why: A tsunami in open water may be under a metre high but hundreds of kilometres long, so it is invisible from a ship yet unmistakable to a pressure sensor.
9In a hurricane forecast, what does the "cone of uncertainty" show?
- A The area that is certain to be struck
- B The region expected to receive the heaviest rainfall
- C The zone where the eye will be visible from the ground
- D The likely range of positions of the storm's centre, not the extent of its effects Correct
Answer: D. The likely range of positions of the storm's centre, not the extent of its effects

Why: The cone is drawn from the average track errors of recent seasons, and damaging wind and surge routinely occur well outside its edges.
10In severe weather alerts, what does a "watch" mean as opposed to a "warning"?
- A A watch covers a smaller area than a warning
- B A watch applies to rainfall and a warning to wind
- C Conditions are favourable for the event, whereas a warning means it is happening or imminent Correct
- D A watch is issued at night and a warning during the day
Answer: C. Conditions are favourable for the event, whereas a warning means it is happening or imminent

Why: The distinction was adopted so people have time to prepare without alerts losing their urgency. Warnings usually cover a much smaller area and a shorter period.

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