November 30, 2025, The Volcano
It is already the last day of November 2025! Some Yellowstone updates below then on to more volcano news…
Look at the link below to check out this last month’s reports from the Yellowstone Volcano Observatory
https://volcanoes.usgs.gov/hans-public/volcano/wy1
Yellowstone’s visitation for the 2025 summer season (June-August) was 2,702,155, based on the total of: 928,250 for June, 975,109 for July, and 881,936 for August. This is an increase compared to the same summer months in 2024 and 2021 (2021 had the highest visitation until this year and 2024 was the second busiest). The numbers for October 2025 have not been released yet, as this was during the shutdown time. Despite that, 2025 is likely to be the busiest summer on record for this area. West Yellowstone was as busy as it gets during the month of October if that is any indication.
During the shutdown, the park did not close to visitors, but no fees were charged as people drove through the gates and staff was limited. As usual, the East, South and West gates closed (to motorized vehicles except administrative use) by Nov 1. ( Those gates will open mid December for over snow travel until mid March). Despite roads being closed to vehicles, we could still ride out bikes on those roads.
By Thanksgiving we had almost no snow on the ground and the ski trails could not be groomed for our Fall Ski Festival. A very rare situation. Some teams came to West Yellowstone anyway and took advantage of snow free roads in the park on roller skis and bicycles.
Now, on to Volcanos…..
Yellowstone, as you likely know, is partially formed by active volcanism. (Glaciation and tectonics are other geologic players in Yellowstone’s landscape today) Volcanism is still at work under the surface of the park, helping create the hot springs, mud pots, geysers and many more features in all the thermal areas exposed on the on the surface. AND impacting life forms that exist in this super hot, super extreme PH and very high mineral and heavy metal content in some locations. What is known about Yellowstone’s volcanics relates to the existence of a magma plume far below the surface that is rooted in the mantle layer of the earth. As the crust (North American Plate) moves to the SW over this semi molten plume, pressure builds. Through the millennia, the perfect combination of pressure, magma and steam have triggered a series of HUGE caldera (collapsed volcano) forming eruptions in a pattern that we can see on the surface throughout the Snake River plain.
The map below is taken from the Yellowstone Volcano Observatory website and is public domain
As you look at the map above, you’ll notice the youngest age (ages marked in the oval shapes indicating calderas) is 2 million years ago. The most recent caldera forming volcano that occurred in this area actually erupted 631,000 years ago and the caldera is about half the size of that 2 million yr old caldera. The “rim” of this more recently formed caldera would overlap the upper right portion of the 2MYA caldera and extend up and to the right beyond, within the boundaries of current day Yellowstone. To the right you’ll see a map of Yellowstone with the Caldera rim outlined (and multiple earthquakes marked in red)
Much of what we observe in Yellowstone is a result of lava flows that occur post eruption. Most of the surface rock in Yellowstone is Rhyolite, similar in composition to Granite. Continual cycles of super heated groundwater flow through the Rhyolite as it is heated by the hot bedrock and rises due to high pressures. Depending what this water encounters on it’s journey back to the surface will dictate how we see it on the surface. It may be a Hot Spring (water flowing without obstruction to the surface) or a Geyser (hot water that hits intense pressure closer to the surface) . It could be Mud Pots that are impacted by Sulphur metabolizing microbes and surface water or perhaps Fumaroles (stem vents) when rising ground water encounters such high pressure it bursts into a gas before reaching the surface. Many, many more signs of volcanism are visible in Yellowstone.
Below you’ll see some photos of another volcano in a US National Park…
The photo above was taken by David Elias the first day of the recent volcanic activity on the Island of Hawaii. The date was Dec 23, 2024. November 25th a few days ago, the 37th episode of lava fountaining occurred! This volcano has been erupting almost one year.
Look at the link below for more info
https://www.usgs.gov/volcanoes/kilauea/volcano-updates
Hawaii Volcano National Park is another hot spot rising from a mantle plume, but in this case, it surfaces on the ocean floor, under thousands of feet of ocean water. This magma is basaltic versus rhyolitic. Rhyolite is more closely related to Granite. Basalt is more dense than Rhyolite or Granite because it has a higher concentration of heavier minerals like iron and magnesium, while Granite/Rhyolite are less dense due to its lighter minerals, such as quartz and feldspar. Much of the ocean floor is Basalt, but it can be found on the continents as well ( Devils Post Pile in California, Giants Causeway in Northern Ireland, the cliffs of the Yellowstone River in Tower Canyon). Volcanic activity in Hawaii will build broad “shield” volcanos rather than collapse into a caldera. These are formed from a may years of more fluid lava flows ( versus explosive gaseous eruptions such as Yellowstone or Mount Saint Helens) that build through the years to form the volcanoes that build to tower from the surface of the ocean and stand above the surrounding landscape. These tend to erupt much more frequently than Yellowstone’s volcanic system. Sometimes a caldera, or crater, will form on the summit of these tall shield volcanos
The hotspot currently under Hawaii is responsible for producing the Hawaiian Ridge-Emperor Seamount chain over the past 80 million years as the oceanic crust has been moving to the north and west. Despite differences in eruptive behavior and outward appearance, Yellowstone and Hawaii have some deeply rooted similarities. They both occur when tectonic plate move over Plumes. Mantle plumes operate independently of plate tectonics and remain mostly stationary as the Earth’s tectonic plates move above them. As a result, magmatic systems like those in Hawaii and Yellowstone produce chains of volcanoes that have an age progression along their lengths. Volcanoes in the Hawaii chain get older the farther northwest you go across the Pacific Ocean from the Hawaiian Islands. Calderas in the Yellowstone Volcanic field get older the farther south and west one travels from current day Yellowstone. The oldest Yellowstone Hotspot triggered caldera is close to the Nevada, Idaho and Oregon boundary. Iceland, Galapagos and the Azores are also islands or island chains due to hotspot activity.
When I visited the island of Hawaii in 2014, this is a sign that had been entombed in a lava flow!
USGS public domain
Most volcanoes around the world are not caused by plate movement over a hotspot. The majority of the world’s volcanos occur along “The Ring of Fire” See image below……..
From the Smithsonian sponsored Global Volcanism Program: The “Pacific Ring of Fire” (PROF) is not a scientific term, but rather a popular description for many areas around the Pacific Ocean with high levels of volcanic activity that originated more than 100 years before the theory of plate tectonics provided a framework to explain the distribution of most volcanoes. While this is an appealing phrase, these areas do not form a single “ring” structure, adjacent volcanoes do not have connected magma reservoirs, and regions have separate tectonic environments. While hot erupted lava is incandescent, volcanic rocks are not on fire or burning, and volcanic ash is actually tiny fragments of rock.
OK, that’s a lot about Volcanos, but I wanted to give you some basic info about hotspot volcanos, versus volcanos that are found close to plate boundaries, such as the Cascade Volcanoes in our Pacific Northwest.
OK, that’s it for now. I wish you all the very best as we approach December, the “holiday season”, winter solstice and everything leading up to a New Year. Leslie lesliehstoltz@gmail.com
PS.. for continuing cool and fun weekly news about the Yellowstone (and sometimes other) geology look at
https://www.usgs.gov/volcanoes/yellowstone/caldera-chronicles