Public domain. Since Yellowstone National Park was founded, the iconic Old Faithful geyser has attracted millions of tourists every year. Although Old Faithful's activity on the surface is well observed and monitored, our current knowledge of the subsurface properties and processes, such as the depth of the plumbing system and how Old Faithful recharges over time, remains largely unknown.
But new research is helping to shed light onto this problem by using seismology to image geysers in much the same way as an MRI is used to image the human body. Seismic signals originating in volcanic systems have often been used to infer the status of magmatic activity.
Similarly, active hydrothermal systems also generate observable seismic signals, called hydrothermal tremor, due to steam bubble formation and collapse. A better understanding of the origin of the hydrothermal tremor can lead to better understanding of the subsurface fluid movement. Most previous work, however, has used just a few seismometers and so does not have the ability to precisely determine the spatial and temporal characteristics of the tremor sources.
With the recent availability of low-cost, easily-deployed nodal seismometers, however, it is now possible to deploy dense seismic arrays close to hydrothermal features and record high-quality hydrothermal tremor signals. When data from these dense arrays, made up of tens to hundreds of stations, are analyzed together, we can image the subsurface with unprecedented spatial and temporal resolution—we can get a four-dimensional 4-D view of a geyser system!
Schematic model showing a cross section of Old Faithful's plumbing system as determined from seismic studies. The red circles t0-t3 show the location of the tremor source over time, and how the tremor source migrates upward prior to an Old Faithful eruption. Times between red circles are based on a minute eruption interval. A geyser is a natural hot spring that erupts with a gush of steam and water. The most famous of these natural wonders, known for its predictability and beautiful plume, is Old Faithful in Yellowstone National Park.
The average interval between its spoutings is 78 minutes. A geyser is the product of heat, water, and some plumbing. The heat comes from partially molten rock, or magma. Underground water is supplied by rain and melting snow that seep through a vast system of cracks and fissures. These same passages provide escape hatches for steam and water exploding upward. Because lodgepole pine trees do not grow on active geyser mounds, the study suggests that when these trees grew on the Old Faithful Geyser mound approximately to years ago, the geyser was not erupting.
In the Yellowstone region, past climate reconstructions based on tree ring records reveal that a severe and sustained drought occurred in the mid th century, which coincides with the onset of tree growth on the Old Faithful Geyser mound.
It would seem, then, that the pause in Old Faithful eruptions during the 13 th and 14 th centuries was related to diminished precipitation and groundwater supply to the geyser for several decades.
The severe 13 th century drought had significant effects well beyond Old Faithful Geyser. In fact, severe and persistent droughts impacted large parts of the USA and had a tremendous impact on indigenous peoples, including the Anasazi , Fremont , and Lovelock cultures. The full length of this sample covers the time period CE. Since climate influences tree growth and the width of annual rings, the relation between ring widths and recent instrumental climate records air temperature, precipitation and river discharge is used to interpret climate variability in the distant past.
Wood from the lodgepole pines was preserved for over years on the geyser mound because it was near-continuously wetted by the alkaline, silica-rich thermal waters erupted from geysers.
These waters deposit the mineral opal on tree stems and wood tissues which prevents the disintegration of cellulose by fungi, bacteria, and insects—it causes silicification , or mineralization, of the wood! This silicification process can be rapid and take only days or weeks. Because climate models forecast increasingly severe regional droughts by the mid st century , results from the new study suggest that geyser eruptions could become less frequent in the future.
Indeed, periods of decreased precipitation have been shown in modern times to result in less frequent eruptions of Old Faithful , and the new research indicates that severe, long-duration droughts can terminate eruptions.
For now, Old Faithful remains just that—faithful, with eruptions occurring about every 90 minutes. But this was not always the case in the past, as the new research demonstrates, and might continue to evolve in the future.
But why. Volcanologists have a variety of ways of measuring present-day gas emissions from volcanoes. But what about gas emissions that happened in years past, before measurements were possible?
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