Old Faithful geyser is one of the most popular areas in Yellowstone National Park. But a major climate event nearly 800 years ago made the geyser a little less faithful. Wyoming Public Radio's Ivy Engel had a conversation with U.S. Geological Survey research geologist Shaul Hurwitz, who studied this strange period.
Shaul Hurwitz: Based on a bunch of different reasons, we think that most of the big geysers in Yellowstone, including Old Faithful, are a few thousand years old. They're post-glacial, that means that after the glaciers receded from Yellowstone about 13 or 14,000 years ago, that's when geysers started forming. But exactly how long after that we don't know and some of them erupted and then stopped. So the same thing with Old Faithful, we don't know when it started but we do know that the last few hundred years, it was erupting relatively constantly.
Ivy Engel: What led you to look at the petrified trees around Old Faithful for evidence of previous eruptions - or, non-eruptions?
SH: So I know that today, for example, there's no trees that grow on active geyser mounds. So when the geysers erupt, the water that splashes on the trees will not let them grow. So any of the geysers in Yellowstone that you go [to], around them there are no trees. I read a paper that was published in the 1950s by a park naturalist describing a tree and some other trees [around Old Faithful]. I didn't know much, but he described a tree and the trees. So I knew that there was something special when that tree was there. The geyser was probably not erupting just by extending from what we know now. So I was curious to know when that tree grew there to understand what were the conditions that led to that tree growing and what was for the geyser then, that is different than it is today. So I applied with several colleagues to the National Park Service. And then when the park approved it, we went out there and sampled those wood and trees.
IE: And what are some of the things you found?
SH: We had a total of 41 samples that we used for radiocarbon dating. And we sent it in two batches. 'Cause the first batch, we sent to the lab and when we got the results, it was one of those too good to be true, all the results kind of clustered within about 100 years. I had to convince myself that that's a real result and not some random results. So I sent another batch and that second batch also came exactly within the same about a 100 year range, which is quite surprising. When you get radiocarbon dates, you have to do some corrections. And after the corrections, everything came to be within about 100 years from about mid 13th to mid 14th century. So that was quite surprising. So I had to find out what were the conditions in the 13th, 14th century. So when I looked at climate really, it ends up that that was just towards the end of a very dry period all over the western U.S., it's called Medieval Climate Anomaly. All the way to California, it was a very sustained, protracted period of droughts. Geysers need water. No water, if it's extreme, probably no eruptions. If it's less water, eruptions can still go on, but be less frequent. So what happened then probably was a very long period of sustained long droughts that caused the geyser not to erupt. And therefore that allowed the trees, which are lodgepole pines, which are very adaptable to occupy the mound for that duration. And then when climate conditions changed again, became a bit more wet, the geyser started erupting, and the trees died, and no more trees grew since.
IE: Do seasonal droughts affect the geyser's eruption or just megadroughts?
SH: At the end of the 20th century, the beginning of the 21st, there were a few years [that] were relatively dry. And when that happened, we could see that the average of the annual interval of Old Faithful, slightly lengthened when there was less precipitation. So we did see that correlation that again, what happened, the geyser didn't stop, but averaged over one year, the eruptions were a few minutes longer - intervals between eruptions.
IE: How does your research relate to current climate predictions?
SH: My research and this paper is trying to say, okay, in response to any climate, but regardless of what the cause is, this is what Old Faithful might do. We rely in our paper on other studies that try to use models to predict the regional climate, and we say if their models would hold, this is what might happen to Old Faithful. But again, if it doesn't hold, this would not happen to Old Faithful. But two of my co-authors in this paper are also from the U.S. Geological Survey. And they are climatologists. They reproduced that 13th century climate based on records that we have. We did not do any extension into the future. That is something that I know it's sensitive. So we just use other models and say, if these models will hold this is what will happen, because, again, the focus of this research was the finding of those trees and understanding why the geyser was erupting, not necessarily on the climate itself, which there's a lot of different paper that shows the effect of that Medieval Climate Anomaly drought that I mentioned.
IE: What does this mean for the future of Old Faithful and Yellowstone in general?
SH: Yellowstone overall draws about, [in the] last few years, about four million visitors a year. And the Park Service has to plan the infrastructure to host these four million that would allow that amount of people to watch the geyser, every eruption. If, as predicted, into the mid 21st century, conditions would be drier and drier, not only would we have more fires in Yellowstone, but it might be that the eruptions of Old Faithful would, for example, lengthen. Intervals would lengthen, not the eruption but the intervals between eruptions. That means that you would have at any given point more people waiting to see the eruptions in the Old Faithful area. So the park service would have to adapt the infrastructure to accommodate that change, for example. That's just one implication. If it goes for a sustained period of a lot of dryness, then maybe we'll get much longer intervals or if it was like in that sustained drought in the 13th century, you might get even cessation if it's really extreme and sustained for a long time.