Back to the AWG Field Trip Page
Yellowstone Field Trip - June 2001
by: Clare P. Marshall, Denver Chapter
|
(Above) The famous Lower Falls on the Yellowstone River, which carved out Yellowstone Canyon. [larger image]
(Below) Tower Falls, named for the volcanic pinnacles adjacent to the water fall. [larger image] |
AWG was fortunate to sponsor a field trip to Yellowstone June 1-4, 2001. Denver Chapter members Katie KellerLynn and Clare Marshall chose the times and (what's even more important) the leaders to make this trip memorable and educational. We asked the leaders to show us the geology of Yellowstone. The thermal features are part of that, but not all, and we wanted to see it all.
The time scale on this trip was interesting to me. On almost every other geology field trip I have attended, the Quaternary rocks are considered "overburden," things that cover up the significant aspects of the story. "Paint it yellow and think about what is below" is the common conviction. But in this area, the most important event happened only 640 thousand years ago. Like many others, I needed to make a mental adjustment, to think in terms of hundreds of thousands rather than hundreds of millions of years of geologic time.
A new term has recently been proposed in Yellowstone: geoecosystem. This new term seems to help nongeologists see the effects that the Earth's rocks and geology have on other aspects of the ecosystem. Most nonscientists and many biologists think of the term "ecosystem" as encompassing the interactions of air, water, flora, and fauna, without considering the ground the flora members are rooted in and the fauna members walk on. Adding the prefix "geo-" to the actually all-encompassing "ecosystem" simply emphasizes that geology is an important aspect as well. Geoecosystem is a redundant word, except for the fact that most people forget about the geology part of an ecosystem.
Paul's multisyllabic vocabulary is a joy to hear. He choses exact words, often subtly tinged with humor. He brings to Yellowstone his love of research and teaching, which was surely enhanced in his prior career as a geology professor and department chairman in Indiana. He demonstrated a wide ranging knowledge and an in-depth understanding about geologic processes in general and Yellowstone in particular. He said that he learns from the experts and incorporates their ideas into his personal philosophy, but that he is not necessarily swayed by their convictions. Paul was good at explaining their "divergent hypotheses" on the complicated Quaternary history of Yellowstone. He was not shy about admitting when he didn't know the answer, although that wasn't often.
So, on Saturday, we learned about the caldera, the big one that was the site of the eruption 640 thousand years ago and that is encompassed within the park. The Yellowstone volcanic field erupted humongous amounts of ash and lava, orders of magnitude more than historic events have produced. Sometimes the source of these volcanic rocks is referred to as the Yellowstone Caldera, but it is officially named the Lava Creek Caldera (after the unit that was extruded at the time of the caldera formation). Outside the caldera, rhyolite ash flows and later basalt flows have been mapped for miles around. Inside the caldera are rhyolitic lava flows (including an obsidian flow) and lots of thermal features, which themselves are kept active by the heat flow and the seismic activity associated with the hot spot under the caldera.
 |
 |
 |
Silicious sinter deposits, sometimes called geyserite, in a flowing thermal spring at the West Thumb Geyser Basin. [larger image] |
The most common thermal feature at Yellowstone National Park is the hot spring. The clarity of this one (at West Thumb Geyser Basin) indicates that it is very hot - too hot for the thermophile bacteria or algae to live. The yellow color in this hot spring is sulfur. [larger image] |
This yellow algae (or bacteria) is one of the more common thermophile (heat loving) life forms in and around the hot springs in Yellowstone National Park. This picture was taken at Rainbow Springs, a large hot spring with many varieties of thermophile bacteria and/or algae making concentric colorations around the spring. [larger image] |
Thermal kames are rounded deposits of sand and gravel that are cemented by hydrothermal deposits along the margins of, or in contact with, glacial ice. The large number of thermal kames in Yellowstone indicate that hydrothermal activity is temporally associated with glaciation, meaning that hydrothermal activity has been going on for tens of thousands of years.
 |
Mud Volcanoes are common throughout Yellowstone National Park; this one is at the West Thumb Geyser Basin. Mud volcanoes are relative dry hot springs which are highly acidic. The acid dissolves the feldspar in the rhyolite bedrock, making clay. The acid also causes the thermophile bacteria to die, so these are usually grey to white. [larger image] |
Toward the end of the day we saw a broad view of the landscape and reviewed some of the things we learned. In particular, we got a better sense of the scale of the caldera. This stop, near Dunraven Pass, focused previous explanations, a good culmination. And, yes, we saw some animals Saturday, including a grizzly bear, trout leaping out of the LeHardy rapids, elk, bison, and birds of every variety. And we learned how animal behaviors depended on the geology, in this beautiful and unusual ecosystem.
 |
(Above) This is a continuous geyser, spouting off at the Firehole Lake just south of our campground along the main road between Madison and Old Faithful. [larger image]
(Below) This hot spring is flowing into the Firehole River. The colors are caused by different varieties of thermophile bacteria and other microscopic life forms. You can distinguish temperatures of water by the color. [larger image] |
 |
The stories about Yellowstone's historic past were fascinating, especially because of his personal experiences (and those of his family). Stories about park policies and how they developed gave us a different viewpoint from the conventional National Park Service gospel. The camp ground was animated with ideas and discussion after his freestyle evening presentation. Animal-encounter stories continued for hours after he left the campfire.
Sunday, Cheryl Jaworowski, Henry Heasler, and Bob Richard led a group in as many as 10 cars around the northern loop of the park. Cheryl and Henry are a spirited wife and husband team of geologists. Cheryl is an instructor of Geoscience at Laramie County Community College in Cheyenne Wyoming, and has led field trips through Yellowstone. She teaches geology, geography, and geographic information system courses. Her research includes Quaternary geology, especially the glacial geology of Wyoming and the relationship with Yellowstone volcanic ashes. Henry is a research professor at the University of Wyoming. He has worked on geothermal systems throughout Wyoming, and currently directs the Wyoming Internet Map Server Project (http://www.wims.uwyo.edu), which includes Yellowstone National Park.
Most of Sunday was spent outside the caldera. Cheryl's enthusiasm for the glacial history of Yellowstone captured us all. Henry told us about the thermal features we saw and the landforms we observed. His talk was sprinkled with historical information as well. Bob pointed out the animals, even a black wolf!
We started the trip with a good map, giving us a foundation to assimilate what we saw Saturday with what we were about to see. Norris Geyser Basin, the hottest thermal field in the park, has a long human history as well as very interesting hot springs and geysers. We did not walk around it as much as we might have because the weather had turned cold and wet. At Mammoth Hot Springs, the tour split up a bit, with most following Cheryl and Henry around the lower loop of the travertine terraces. This hot spring is hydrologically connected to Norris Geyser Basin, the water traveling along fractures through volcanic rocks and limestone. The terraces deposit calcium carbonate in the microcrystalline form of travertine. The only large travertine deposits in the park are located here. Most of the group then participated in a "tailgate" party for lunch; the backs of three Subarus were used for food distribution.
 |
Our Leaders on Sunday: Bob Richard, Cheryl Jaworowski and Henry Heasler. Speaking at the Lamar Valley stop. [larger image] |
The trip ended with many of the campers leaving the campground for hot showers and hotel rooms, because of the snow. Many participants took the opportunity to view the famous hydrothermal features independently, armed with an excellent geologic understanding given to us by our leaders. It was a really good trip.
