Caldera Chronicles: A Do-It-Yourself Guide to Estimating the Height of Geyser Eruptions | national news
Chronicles of the Yellowstone Caldera is a weekly column written by scientists and collaborators at the Yellowstone Volcano Observatory. This week’s contribution is from Mark Wolf, a seasonal physical science technician on the Yellowstone National Park Geology team.
Estimating the height of the eruption by looking at a geyser can be difficult for several reasons. There is often no reference object in the immediate vicinity of the geyser, which can confuse our perceptions.
Likewise, although you can get an idea of the height of a skyscraper by the size of the windows at the top, the water droplets sprayed into the air from a geyser are not as good as a reference. Not to mention the fact that the droplets start to fall as soon as they reach their peak, and unlike a building or a tree, the water fountain does not yet hold.
However, by borrowing a relatively simple technique used in fields like forestry, astronomy, and geodesy, anyone can measure the height of a geyser eruption with reasonable accuracy. For those who may have wondered during high school math class when you need to remember and use the phrase “SOH-CAH-TOA”, now is the time!
For this method, the only measurement that needs to be taken during the rash itself is called the tilt angle. This is the vertical angle above the horizon (looking directly towards the horizon is 0 degrees and looking directly above your head is 90 degrees).
To get this measurement, you can use a homemade “clinometer” made up of a protractor and a weighted string, or you can purchase one (these are typically used in forestry or surveying). There may even be a clinometer or theodolite app on your smartphone. Whatever instrument you use, make sure it is calibrated before use.
When the eruption begins, point your instrument towards the top of the water shards and record the angle. This part may be trickier than it looks. It is difficult to tell what the “peak” of a geyser is because the jet diffuses in small droplets and the flowing vapor can obscure your view. Use your best judgment and try to measure multiple bursts in the same rash.
After determining the tilt angle (α) of the rash, you only need two more measurements to convert that angle to height. This is your horizontal distance from the geyser (x) and your vertical distance from the geyser vent (y1). Since it would be dangerous (and illegal) to leave the boardwalk and use a tape measure, you can use a map to determine these numbers – Google Earth, for example, works great.
A more accurate, albeit expensive, method is to use a device called a range finder, which uses a laser (and trigonometry) to determine the two distances. Once you have these numbers, it’s time to “SOH CAH TOA”:
y2 = x ∙ tan α
height = y2 + y1
(You might want to do additional measurements and calculations if the spray leaves the ground at an angle, but we’ll leave that for another time.)
Whichever method you use, it helps to plan ahead – where are you going to stand to see the geyser eruption? – so that you can be prepared with the distance measurements. Keep in mind that you don’t necessarily want to be as close to the geyser as possible to get a good measurement. Stand back a bit to easily see the entire water column. It also helps to do this on a clear, sunny day, and if it’s windy, find a place upwind of the geyser.
Regardless of the method, there will always be some degree of uncertainty. More technology could be used to determine the height of the rash, but the increased precision and accuracy might not be worth it.
Get out there and try measuring some of these amazing features the next time you’re in the park. You can practice ahead by measuring a building, tree, or maybe even fireworks. It’s always good to see if your measurements are repeatable.
When in Yellowstone, it would be good to try and measure one of the predictable geysers, but you can also try your luck (and your patience) by trying to measure the so-called ‘tallest geyser currently active in the world’ – Steamboat Geyser in the Norris Geyser basin.