Montana’s autumn is my favorite time of the year to do field work. Daytime temperatures are usually cool enough to encourage one to keep moving and the lighting is simply gorgeous. It is also one of the best times to visit areas in and around Yellowstone National Park (YNP) because most of the tourists have gone home. So no huge bear traffic jams or jostling for parking spots at the better known thermal spots in YNP and surrounding environs – it’s just a wonderfully introspective time for field forays. What follows are several photos that chronicle some of my fall wanderings in the greater Yellowstone area, both in terms of wildlife and geology.
Some of my favorite sightings in YNP are bison at any time of the year. But the autumn snows bring on the bison’s technique of using its head to clear snow away from any vegetative food source. The result of their snow-clearing activity is a snow-masked face.
And where the snow hasn’t stacked up much, the YNP bison calmly graze and occasionally congregate on a ridge line to watch what remains of the YNP visitor traffic.
Geological features in YNP take on new dimensions with the golden low and slanting light of autumn. I’ve spent much time re-photographing geologic features at all scales that seem to glow in this season’s light.
The fall staging areas of sandhill cranes in southwestern Montana are mesmerizing. Staging areas are those locations where cranes annually congregate during late September into October, spend several days foraging through fields for food, and eventually continue on their migration southward from Montana to Colorado and the southwestern U.S.. The staging area that I usually go to is near Dillon, Montana, where hundreds of cranes can be viewed.
As I said initially, it’s hard to surpass a Montana/YNP autumn!
Geologic field work is always fun, but especially so when it turns up something unexpected. Working on Eocene to Recent geology and vertebrate paleontology in the Gravelly Range, southwestern Montana promised to be enthralling because the volcanics, sedimentary units, and vertebrate fossils are at elevations of about 9,000 feet. But to come across extensive, unmapped calcareous spring deposits of probable Eocene age is topping off research efforts.
At this point, I’ll just say that our field team is still at work on the Tertiary spring deposits. We’ve found numerous leaf impressions including those of ginkgo, palm, metasequoia, Fagopsis (extinct member of Beech family), and alder – just to name a few. We’ve shown the plant assemblage collected to date to several paleobotanists, and, at least for age, their take is that the assemblage is probably latest Eocene in age, and bears many similarities to Florissant, Colorado fossil plant assemblages.
The spring deposits in the Gravelly Range are extensive, covering an area roughly 2 miles in length with deposits up to 120 feet in thickness. The springs are best characterized as travertine, although the spring systems’ edges contain clastic fluvial units and both the springs’ edges and pools have features such as plant impressions, root systems, and small travertine balls.
Because the Gravelly Range is so close to Yellowstone National Park, it is extremely interesting to compare its Eocene spring deposits to hydrothermal units at both the currently active Mammoth Hot Springs (which probably began its activity about 7,700 years ago), and to the fossil travertine found just north of Gardiner, Montana, that formed about 19.500 to 38,700 years ago (Fouke and Murphy, 2016: The Art of Yellowstone Science: Mammoth Hot Springs as a Window on the Universe).
The Gardiner travertine is fairly well exposed because it has been extensively quarried for several decades. Of interest for comparison are numerous plant impressions that occur within microterracettes. Fouke and Murphy (2016) suggest that these may be impressions of sage brush. A photo of the quarried wall with the plant impressions is shown below.
Other features in the Gardiner travertine, now partly covered by graffiti, include a quarry wall that shows terracettes and microterracettes that are outlined by darker lines within the travertine. These features are probably indicative of a proximal slope facies.
Jumping forward in time to the extensive spring deposits of Mammoth Hot Springs (just within the northeast park boundary of Yellowstone National Park), is mind boggling. As in any comparison with rocks as old as Eocene to active deposition, one realizes how much detail is lost over time. But it is still worthwhile to try to compare spring features, so I’ll show a few photos of the Mammoth Hot Springs that may match up with various features of the fossil springs.
Suffice it to say, that the upcoming field season should be a good one, with more work to be done on the Gravelly Range spring deposits. And – it’s always fun to get a trip in to Yellowstone!
Some winter days in Yellowstone National Park are so amazing with clear blue skies and sparkling snow that they just take your breathe away. Luckily enough, I just experienced several of these kinds of days which I packed full of cross country skiing, snowshoeing, and animal watching.
One of the groomed trails that held a good snow base until about early afternoon is the Blacktail Plateau Loop. The trail follows melt-water channels that are associated with “Retreat Lake”, which was formed by the Beartooth glacial ice mass blocking the lower end of the Grand Canyon of the Yellowstone during the Pleistocene.
The Tower ski trail provides access to the Grand Canyon of the Yellowstone area. A favorite stop of mine is the Calcite Springs overlook where the thermal springs lie south of the overlook, on the west side of the Yellowstone River and Pliocene/Pleistocene sediment and basalt are on the Yellowstone River’s east side.
A groomed ski trail also accesses the Upper Terraces of Mammoth Hot Springs. However, after a few days of spring-like temperatures, the snow was so melted back that I just used my snowshoes to trek through the icy slush. Some thermal features were still covered by snow and slush, but others appeared much more vibrant against the white snow/slush blanket.
Aphrodite Terraces lie a short way north of the White Elephant Back Springs:
My favorite thermal feature of the Upper Terraces is Orange Spring Mound. The spring is supported by a fissure ridge and is intermittently active. Because of its low water discharge and subsequent slow growth, it has built up a characteristic cone shape.
All in all, it was perfect wintertime fun trekking around in Yellowstone. Can’t wait to get back there when the bears come back out from hibernation!
Volcanic stratigraphy is hard to ignore when touring through the Teton to Yellowstone National Parks (YNP) area. Three major volcanic eruption cycles occurred during the last 2.1 million years and resulted in hundreds of feet of volcanic rock. The eruption cycles make a good basis for separating the volcanic rock units and consequently there are three major volcanic stratigraphic units. These major units consist of ash-flow tuffs that erupted at the peak of each cycle and include the Huckleberry Ridge Tuff with an age of 2.1 million years, the Mesa Falls Tuff with an age of 1.3 million years, and the Lava Creek Tuff with an age of 0.64 million years.
The type sections of the Huckleberry Ridge Tuff and the Mesa Falls Tuff are fairly accessible. The Huckleberry Ridge Tuff type section sits at the head of a large landslide about 1.5 miles south of the YNP’s south gate and 1 mile northeast of the Snake River Bridge. It’s a big landslide, so it’s easy to spot from the highway. The type section mainly contains welded rhyolitic ash-flow tuff. This huge eruptive event (one of the five largest individual volcanic eruptions worldwide) associated with the Huckleberry Ridge Tuff formed a caldera more than 60 miles across.
The Mesa Falls Tuff type section is really accessible as it is alongside Highway 20, about 3 miles north of Ashton, Idaho. The type section consists of airfall tuff, partially welded tuff that has an agglomeratic base. The eruption associated with the Mesa Falls Tuff formed the Henrys Fork Caldera which is in the Island Park area west of YNP.
The Lava Creek Tuff type section is much more difficult to access as its type section in the upper canyon of Lava Creek, about 8 miles into the backcountry of YNP. There are a couple reference sections that are easier to reach, and one is in Sheepeater’s Canyon, about 0.5 miles northeast of Osprey Falls. The Lava Creek Tuff is also readily seen in the south-facing cliffs along much of the Gibbon River. The eruption associated with the Lava Creek Tuff created the Yellowstone Caldera, the 35-mile-wide, 50-mile-long volcanic depression that dominates the present YNP landscape.
There are many more volcanic units associated with the three major eruptive cycles. But spending time looking at the major ash-flow tuff units is a good way to begin to delve into Yellowstone geology.
Last Thursday (July 10),Yellowstone National Park (YNP) temporarily closed the 3.3 mile-long Firehole Lake Drive, a paved road that traverses some of Lower Geyser Basin. Melting asphalt on a part of the road near the start of the loop drive became a “soupy mess”, according to Dan Hottle, YNP spokesman. Hottle told Live Science that Firehole Lake Drive’s surface reached 160° Fahrenheit (70° Celsius) on Thursday, roughly 30° to 40° F (17° to 22° C) hotter than usual. Hot gases from area thermal activity that were trapped by the asphalt road surface and warm weather combined to cause the road damage.
YNP said that the road would reopen soon and sure enough, by the time I was there on Monday (July 14), the road was driveable. One of the YNP information rangers at Canyon Village told me that the road repairs included road crews removing damaged pavement and applying a mixture of sand and lime to soak up some of the thick bubbly road oil. The road section was then graveled so that the hot gases could better escape a more permeable road surface.
Thermal activity affecting YNP roads and parking areas is not uncommon. During my Monday travels in Yellowstone, another Canyon area YNP ranger told me that about 10 years ago, a new thermal feature melted a small part of the Mud Volcano parking lot. This area is now fenced off, but the rest of the parking lot is still used. YNP spokesman Hottle also informed Live Science that YNP has closed Firehole Lake Drive in the past for repairs due to heat damage, but that these closures are not frequent.
And – just for some perspective on this latest road meltdown: the YNP website home page says “Yellowstone contains approximately one-half of the world’s hydrothermal features. There are over 10,000 hydrothermal features, including over 300 geysers, in the park”. Given the profusion of thermal activity, I’m not surprised that a small section of asphalt melts once in a while. I guess I’m amazed that the YNP can keep park infrastructure maintained such that millions of people can visit the park every year.
Living near Yellowstone National Park has its advantages – and the best of these is being easily able to go on field trips to the Park area. A field trip opportunity came up last week when the Rocky Mountain section of the Geological Society of America came to Bozeman, Montana, for its annual meeting. One of the meeting field trips was the “Glacial and Quaternary geology of the northern Yellowstone area, Montana and Wyoming”. The trip was led by Ken Pierce, Joe Licciardi, Teresa Krause, and Cathy Whitlock. Having spent much time in the Yellowstone area, I was ecstatic about going along to find out about recent geological work. I won’t elaborate on the specifics of the trip, but for those interested in more than the photos posted below, the field trip guide is available in The Geological Society of America Field Guide 37, 2014, p. 189-203. It’s worth a read!
A few of the stops on the trip:
Paradise Valley – Chico Moraines and Chico Outwash (45.3402 N, 110.6967 W)
North Gardiner Area – Giant Ripples (45.0551 N, 110.7659 W)
I give much thought to supervolcanoes – mainly because I live next to Yellowstone National Park and consequently spend much time in the Park. So when I saw today’s Nature publications about the cause of super-eruptions, naturally I wanted to read them.
I’ll first start with a definition for a supervolcano, and for that I’ll use one given by the U.S. Geological Survey:
The term “supervolcano” implies a volcanic center that has had an eruption of magnitude 8 on the Volcano Explosivity Index (VEI), meaning the measured deposits for that eruption is greater than 1,000 cubic kilometers (240 cubic miles). The VEI scale was created as a general measurement of the explosivity of an eruption. There are multiple characteristics used to give an eruption its VEI allowing for the classification of current and historic eruptions. The most common criteria are volume of ejecta (ash, pumice, lava) and column height. All VEI 8 eruptions occurred tens of thousands to millions of years ago making the volume of ejecta or deposits the best method for classification. An eruption is classified as a VEI 8 if the measured volume of deposits is greater than 1,000 cubic kilometers (240 cubic miles). Therefore a supervolcano is a volcano that at one point in time erupted more than 1,000 cubic kilometers of deposits.
Now to today’s online Nature publications for the cause of the eruption. There are two publications and each research team uses a different technique which results in finding two distinct causes for eruptions.
We find that the rate of magma supply to the upper crust controls the volume of a single eruption. The time interval between magma injections into the subvolcanic reservoir, at a constant magma-supply rate, determines the duration of the magmatic activity that precedes eruptions.
Here we use synchrotron measurements of X-ray absorption to determine the density of silica-rich magmas at pressures and temperatures of up to 3.6 GPa and 1,950 K, respectively. We combine our results with existing measurements of silica-rich magma density at ambient pressures, to show that magma buoyancy can generate an overpressure on the roof of a large supervolcano magma chamber that exceeds the critical overpressure of 10–40 MPa required to induce dyke propagation, even when the magma is undersaturated in volatiles. We conclude that magma buoyancy alone is a viable mechanism to trigger a super-eruption, although magma recharge and mush rejuvenation, volatile saturation, or tectonic stress may have been important during specific eruptions.
As I said earlier, my proximity to Yellowstone has certainly made me take note of research relating to supervolcanoes. So I’m always glad to find ongoing work on them as well as their triggering mechanisms. Hopefully, better overall understanding of supervolcanoes will expand our capability to predict their super-eruptions.