Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Annie Carlson, Research Coordinator at the Yellowstone Center for Resources, Yellowstone National Park.

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Yellowstone is not your average volcano. Rather than forming a classic cone-shaped mountain like Mount Fuji or Mount Rainer, Yellowstone is different. When it erupts, it has the potential to form huge calderas many miles wide. Thus, visitors to the park are sometimes confused because they can't see the volcano, at least not in the way they might expect. Because it is somewhat unusual, it has taken many decades for us to wrap our heads around Yellowstone's volcanism. Looking back at early accounts of the volcano allows us to appreciate how our understanding has changed over time.

One of the earliest written records of the Yellowstone volcano comes from James Wilkinson, the Governor of the newly purchased Louisiana Territory. In 1805, he wrote a letter to President Jefferson in which he spoke of a map drawn onto a bison pelt by a Native American. Wilkinson wrote about the map, "Among other things a little incredible, a Volcano is distinctly described on the Yellow Stone River." Undoubtedly, knowledge of the Yellowstone volcano existed for thousands of years prior to the written record.

The 1804-1806 Lewis and Clark expedition did not actually pass through the landscape that is now Yellowstone National Park. But when the expedition was returning east, one member, John Colter, opted to remain in the west. With a solo journey during the winter of 1807-1808, Colter is considered to be the first European American to see the wonders of Yellowstone. Many mountain men and fur trappers would follow, and tales of the region spread. In 1851, mountain man Jim Bridger described the Yellowstone area to the Jesuit priest Pierre Jean DeSmet. The resulting Bridger-DeSmet map notes a "Great Volcanic Country about 100 miles in extent" between the Firehole River and Yellowstone Lake.

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Relying on information provided by trappers, formal expeditions were initiated beginning in 1869. The following year, the famous Washburn expedition spent several weeks exploring the landscape, with a few mishaps along the way. On August 29, 1870, several members of the Washburn expedition climbed to the summit of a prominent peak south of Tower Fall. In his report to Congress, Lieutenant Gustavus Doane wrote this of the Yellowstone caldera: "Observations were taken from the summit of the peak which we named Mount Washburn… Turning southward, a new and strange scene bursts upon the view. Filling the whole field of vision, and with its boundaries in the verge of the horizon, lies the great volcanic basin of the Yellowstone. Nearly circular in form, from fifty to seventy-five miles in diameter, and with a general depression of about 2,000 feet below the summits of the great ranges which forms its outer rim… The great basin has been formerly one vast crater of a now extinct volcano."

As we now know, the Yellowstone volcano is not extinct, but it is understandable that early explorers had some misinterpretations about the landscape. Of note, Doane also wrote in his report, "The surface formation of Mount Washburn on the northern or outside slope is a spongy lava." In fact, Doane was standing atop the eroded remains of a 50-million-year-old Eocene volcano while peering down into the caldera formed 631,000 ago by the presently active volcano. How confusing! It would be many years before scientists would provide a more precise timeline to the regional volcanism.

Additional pieces of the puzzle were provided the next year by the Hayden expedition of 1871, which greatly enhanced our scientific understanding of Yellowstone. Expedition members included geologists, a mineralogist, a topographer, and also photographer William Henry Jackson and artist Thomas Moran. The resulting photographs, sketches, and paintings brought the first images of the Yellowstone volcano to the broader public. Ferdinand Hayden compiled a 500-page report detailing their findings, and he actively promoted the creation of a public park.

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Soon after, in December 1871, a bill was introduced for the establishment of Yellowstone National Park. From the House Committee on Public Lands report: "This whole region was, in comparatively modern geological times, the scene of the most wonderful volcanic activity of any portion of our country. The hot springs and the geysers represent the last stages—the vents or escape pipes—of these remarkable volcanic manifestations of the internal forces." Thus, on March 1, 1872, President Grant signed the bill into law establishing a massive volcano as the world's first national park.

Our modern understanding of Yellowstone volcanism was initiated by the doctoral investigations of Joe Boyd in the 1950s and subsequent geologic mapping led by Bob Christiansen. Now scientists from the Yellowstone Volcano Observatory and many other institutions continue to reveal new and exciting discoveries. With such a vast and dynamic landscape, we still have much to learn about the Yellowstone volcano.

(Many of the historic accounts described in this article were compiled by Yellowstone historian Aubrey Haines.)