Volcano Geodesy 101

gps-goin2moon.jpg Rob R. asks:

I’ve been following along with the recent happenings at Yellowstone (that is, as best as I can as a layman) but haven’t seen that site [data from the Yellowstone GPS network] before. Could you explain (or link to) what I’m seeing there and what a “change in surface topography” might look like? Thanks in advance.

Sure thing! What you are looking at on that page is a network of GPS receivers cemented to various points in the Yellowstone caldera and surrounding area. The USGS has written a nice overview of GPS and other geodetic volcano monitoring techniques, and I won’t duplicate their efforts here.

The instrument in this photo is the GPS station from White Lake, Wyoming. For the past several years, it’s been moving upwards at a rate of about 4 cm/yr – if it keeps going, which it obviously won’t, it would take about 10 billion years to get to the moon.

This is the cartoon version of what it is looking for:


It’s not just an expanding magma chamber that will produce this kind of surface change, though. You can also use long-term GPS series (and other types of survey data) to see ground water levels going up and down, the crust gradually relaxing after an earthquake, and the slow creep of plate tectonics.

As for what actual GPS data from an eruption might look like, well, here’s an example from the 2005-2006 eruption of Augustine, in Alaska:


Figure source: Mattia et al., 2008

The space between the dotted lines represents 5 cm of movement. The different colors of dots represent different kinds of data processing; the red ones are the current “gold standard” daily averages.

GPS data is very noisy, compared to the signals earth scientists are looking for. This is in large part due to fluctuations in atmospheric conditions which slow down or speed up the signal in an unpredictable way. One way people get around the noise is to use data acquired over a long period of time, hoping that the weather will cancel itself out. Another is to compare the station of interest to a nearby reference. The Alaska Volcano Observatory has been experimenting with ways of getting reliable positions using an hour or less worth of data, which will enable them to detect changes in the ground surface much more quickly than currently possible with GPS.

  • Mario Mattia, Mimmo Palano, Marco Aloisi, Valentina Bruno, Yehuda Bock (2008). High rate GPS data on active volcanoes: an application to the 2005-2006 Mt. Augustine (Alaska, USA) eruption Terra Nova, 20 (2), 134-140 DOI: 10.1111/j.1365-3121.2008.00798.x


  1. Kim wrote:

    That cartoon rules.

  2. Rob R. wrote:

    Thanks, Ms. Brumm. Love the cartoon version, too. Definitely more my speed. With respect to my original question regarding data from the Yellowstone GPS network, I was wondering if those icons changed in a certain way showing the changes in surface topography you mentioned. Basically, I was just wondering how to read/interpret the page. I’m off to read the ‘overview’ link to gave.

    Very cool of you to take the time to explain things like this (was a little nervous about asking a dumb layman question around here.) Thanks again.


  3. Maria wrote:

    Rob, if you click on a station on that overview map, you’ll be taken to a time series of data (which, I don’t actually know how often they update it – looks like the last one was sometime in December).

    There are summary maps, too, where the stations are shown with arrows – the length of the arrow is proportional to how fast the station has been moving over the past 3 years. You can see 3 stations that are moving up very fast, and away from each other – indicates that the resurgent dome in that area is, well, resurging.

  4. Rob R. wrote:

    :slaps forehead:

    Thanks, Maria! I never even noticed the icons were clickable. Now that I’ve clicked them I can understand how they tie into Ms. Brumm’s explanation. I was just sitting there like a moron waiting for the page to update and the icons to change. lol.

    Thanks again. Again.


    While I’m already here bugging you guys: I understand that there is some (legitimate?) concern that the ‘up swell’ can cause cracking (faults?) and that, combined with the recent activity, might be creating a ‘chimney’ allowing the lake water to enter the magma chamber possibly creating an explosion (steam/pressur?) which may or may not blow the ‘lid’ off the caldera. That’s why I was interested in understanding the site in question.

    Just hype, or is that a real concern at the moment? Or, am I not even wrong here?

  5. Silver Fox wrote:

    I’m with Kim: that’s one hell of a cartoon!

  6. Andrew Ironwood wrote:

    Just to prove I can avoid being a persnickety old $#!+, I won’t even bring up including the long-term decay in the moon’s orbit into that ’10 billion years’ calculation [blows good-natured raspberry before skipping off into the sunrise, scattering dandelion seeds like confetti in an homage to Rip Taylor…]

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