Measuring Floods and Tsunamis
In this video, Dr Claire Earlie compares tsunamis and floods with their extreme equivalents.
In order to make a comparison between floods/tsunamis and their extreme equivalents we need some kind of measure for both.
Measuring Floods
Measuring the volume of water (discharge) that flows by per second is a good way of judging the size of floods. This measure allows us to determine the depth of flowing water, the area the water covers and the power or velocity of the flowing water.
Diagram of Cross Section by USGS, Public Domain
Megafloods
In the video we compared the 2010 Pakistan floods and a megaflood caused when the Eyjafjallajökull volcano erupted in Iceland. Maybe you were surprised to find out that the Pakistan floods were actually larger than the Icelandic megaflood?
Using the measure we’ve outlined above we can add another megaflood we’ve looked at to broaden the comparison.
| Event | Discharge |
|---|---|
| 2010 Eyjafjallajökull, Iceland megaflood | 3,000 cubic metres per second |
| 2010 Pakistan floods | 47,500 cubic metres per second |
| Dover straits megaflood | 1,000,000 cubic metres per second |
As you can see the Dover straits megaflood vastly outstrips the Pakistan floods and highlights how, when we look at these events over geological timescales, we’ll see how megafloods are truly extreme events.
Measuring Tsunamis
Tsunamis are typically measured by the size of the wave. In the diagram below we can see how the tsunami wave height is measured by reference to the sea level around it. The height of the tsunami results in a greater amount of water being carried to the shore, this is represented by flow depth in the diagram
Diagram illustrating some terms used for tsunami measurements by USGS, Public Domain
Megatsunamis
In the video, we also saw how a regular tsunami was larger than a megatsunami. However, just like floods let’s use the measure we’ve described above and add some other events that we looked at earlier.
| Event | Wave height |
|---|---|
| 1903 Upper Arrow Lake, Canada megatsunami | 3 metres |
| 2011 Tohoku, Japan tsunami | 7 metres |
| Storegga Slide megatsunami | 30 metres |
| Chicxulub impact megatsunami | 100 metres |
This provides a stark example of just how extreme megatsunamis and megafloods are when viewed over geological timescales.
These events have had a significant impact on our planet and help us to understand Earth’s history.
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