[Rockhounds] Geologically speaking, things are always changing at Yellowstone

[Kreigh Tomaszewski]

The summer of 2024 was a busy time, with July’s
<https://www.usgs.gov/observatories/yvo/news/july-23-2024-hydrothermal-explosion-biscuit-basin>hydrothermal
explosion <https://www.usgs.gov/glossary/volcano-hazards-program-glossary> at
Biscuit Basin and the first hydrothermal explosion ever recorded by
geophysical monitoring data
<https://www.usgs.gov/observatories/yvo/news/a-small-hydrothermal-explosion-norris-geyser-basin>
in
Norris Geyser Basin. In addition to these higher energy events, a new
hydrothermal feature popped up right in front of our eyes—literally!

Looking south from near a pullout along the Mammoth to Norris road just
north of the Nymph Lake overlook. On the other side of the marsh is a
tree-covered rhyolite
<https://www.usgs.gov/glossary/volcano-hazards-program-glossary> lava
<https://www.usgs.gov/glossary/volcano-hazards-program-glossary> flow, and
at the base of the flow is a new thermal
<https://www.usgs.gov/glossary/volcano-hazards-program-glossary> feature
marked by a plume of steam and that formed in early August 2024.   Photo by
Mike Poland, USGS, September 1, 2024.

While driving south from Mammoth Hot Springs towards Norris Geyser Basin
early on August 5 last summer, a park scientist noticed a billowing steam
column through the trees and across a marshy expanse. The eagle-eyed
scientist notified the park geology team to verify if this was indeed new
activity.

This new hydrothermal feature is within a region called the Roadside
Springs thermal area, which is a collection of spatially distinct areas of
altered rock and hydrothermal features (data for Yellowstone thermal areas
is at https://data.usgs.gov/datacatalog/data/USGS:661d5eb7d34e7eb9eb7e3a41).
This new feature is at the foot of a rhyolite lava flow
<https://www.usgs.gov/glossary/volcano-hazards-program-glossary> about 3
meters above the marsh below, and it lies within a swath of warm,
hydrothermally altered ground that is approximately 60 meters (about 200
feet) long.

Soon after it was identified, park geologists trudged through the marshy
ground to get a closer look that the feature, which had a temperature of 77
°C (171 °F). A very thin veneer of grey silicious clay barely covered the
surrounding surface, indicating its very young nature.

https://www.usgs.gov/observatories/yvo/news/yellowstone-where-theres-always-something-new