Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week’s contribution is from Michael Poland, geophysicist with the U.S. Geological Survey and Scientist-in-Charge of the Yellowstone Volcano Observatory, and Jeff Hungerford, Park Geologist with Yellowstone National Park.<\/p>\n
Lidar shaded relief map of the Porcelain Basin and Back Basin areas of Norris Geyser Basin in Yellowstone National Park.\u00a0 Orange star indicates the location of a new thermal pool that formed sometime during late December 2024 to early February 2025.<\/p>\n
On April 10, 2025, geologists from Yellowstone National Park were conducting routine maintenance of temperature logging stations at Norris Geyser Basin\u2014their first such visit to the area since the previous fall.\u00a0<\/p>\n
When what to their wondering eyes did appear, but a blue water spring that was new since last year!<\/p>\n
The new pool they found pool is located in the Porcelain Basin subbasin of Norris Geyser Basin, immediately west of a patch of vegetation informally known as \u201cTree Island.\u201d\u00a0It is about 4 meters (13 feet) across, and the water in the pool was warm (about 43 \u00b0C, or 109 \u00b0F), light blue in color, and about 30 centimeters (1 foot) below the rim.<\/p>\n
They spoke not a word and went straight to their work, as this was a job that they would not shirk.\u00a0<\/p>\n
The geologists found that the pool was surrounded by numerous small rocks up to 30 centimeters (about 1 foot) across, and the rocks themselves were covered by light-gray, fine-grained, sandy mud.\u00a0 There also appeared to be two layers exposed in the sides of the pool, but the lower \u201clayer\u201d was just a coating left on the steep side of the pool when the water was at a higher level.<\/p>\n
With all of this evidence of quite a commotion, they knew they had found a hydrothermal explosion!<\/p>\n
That there might have been a hydrothermal explosion at Norris Geyser Basin is not surprising, given that the thermal basin has been the site of numerous such events.\u00a0 Some, like a crater in The Gap subbasin<\/a>, probably occurred before people were documenting the area and have an unknown age.\u00a0Others, like the 1989 explosion of Porkchop Geyser<\/a>, were well observed.\u00a0 And thanks to a new monitoring station installed in September 2023<\/a>, explosions can now be detected by geophysical data, including an explosion in the Porcelain Terrace area in April 15, 2024<\/a>, that left a crater a few meters (several feet) across.<\/p>\n View looking northwest at a new thermal pool in the Porcelain Basin area of Norris Geyser Basin, Yellowstone National Park, that probably formed in a series of mildly explosive events between late December 2024 and early February 2025.\u00a0 The rocks and white material (silica mud) surrounding the pool were probably ejected as the feature formed.\u00a0 The pool is about 4 meters (13 feet) across.\u00a0 U.S. Geological Survey photo by Mike Poland, May 12, 2025.<\/p>\n Animated GIF of high-resolution satellite images of the Porcelain Basin area of Norris Geyser Basin, Yellowstone National Park, showing the development of a new thermal pool in the circled area.\u00a0 There is no indication of the pool in images from October 19 and December 19, 2024.\u00a0 A small depression is visible in the January 6, 2025, image.\u00a0 In the February 13, 2025, image, the pool is fully formed.\u00a0 Imagery processed by R. Greg Vaughan (USGS), and data were collected by the WorldView satellite system and made available thanks to the NEXTVIEW End User License Agreement between Maxar (formerly DigitalGlobe, Inc.), which supports Earth science research and applications.<\/p>\n So when did this feature near Tree Island form?\u00a0 Might it have been associated with an earthquake swarm?<\/p>\n One tool that can be used to investigate thermal changes at Yellowstone is high-resolution satellite imagery<\/a>.\u00a0 Although these data aren\u2019t useful at night or during cloudy conditions, the daytime, cloud-free images provide exceptional views of the ground.\u00a0 The satellite data indicate that there was no feature present on the west side of Tree Island prior to December 19, 2024.\u00a0 By January 6, 2025, a small depression had formed in that area.\u00a0 An image from February 13, 2025, shows the water pool, indicating that the feature had fully developed by that time.<\/p>\n Another helpful tool for assessing hydrothermal activity in Norris Geyser Basin is the new monitoring station that was installed in September 2023 and that uses infrasound<\/a>\u2014low frequency acoustic energy\u2014to detect hydrothermal activity.\u00a0 Not only can infrasound arrays \u201chear\u201d explosions, but they can also tell the direction from which the sound originated!\u00a0 Interestingly, there were no strong and unambiguous explosion signals during the time over which satellite imagery indicate the feature formed.\u00a0 There were, however, several low-level acoustic signals that came from the direction of the new feature.\u00a0 The most obvious such signal was recorded on December 25, 2024, but it was relatively weak, and there was no associated seismic signal\u2014something that would be expected from a significant explosion.\u00a0 Similar acoustic signals were recorded on January 15 and February 11, 2025, but again there were no seismic signals.<\/p>\n What does this combination of data all mean?\u00a0 Could it be used to investigate the scene?<\/p>\n Clearly the new thermal feature did not form in a single major explosive event, like the one of April 15, 2025, in Norris Geyser Basin<\/a> or the well-observed event of July 23, 2024, at Biscuit Basin<\/a> near Old Faithful.\u00a0 Rather, it appears that the feature formed via multiple small events that initially threw rocks and later threw silica mud a short distance, creating a small pit that became filled with silica-rich water.\u00a0 The feature probably started to develop on December 25, 2024, with further activity occurring in mid-late January and early February 2025.<\/p>\n