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Archive for the ‘Geology’ Category

Among the many geographical features that Lewis and Clark were on the lookout for during their transcontinental trip was evidence of volcanic activity. Based on burned-out pieces of lignite coal that floated down the Missouri River, rumors of volcanoes in the Louisiana Purchase territory had reached Thomas Jefferson. Jefferson was intrigued enough to purchase a copy of Claude Nicholas Ordinare’s Histoire naturelle des volcans in preparation for Lewis and Clark’s journey.

Illustration of a 19th century volcano eruption

Illustration of a 19th century volcano eruption

Still, the science of volcanology was still in its infancy, and Lewis and Clark were uncertain what to look for. On August 24, 1804, the Corps of Discovery was passing through present-day Dixon County, Nebraska, when Clark noted the “Great appearance of Coal” in the area  and investigated a burning bluff:

Some rain last night, a Continuation this morning; we Set out at the usial time and proceeded on the Course of last night to the (1) Commencement of a blue Clay Bluff of 180 or 190 feet high on the L. S. Those Bluffs appear to have been laterly on fire, and at this time is too hot for a man to bear his hand in the earth at any debth, gret appearance of Coal. An emence quantity of Cabalt or a Cristolised Substance which answers its discription is on the face of the Bluff—

The area Clark visited was later known as the “Ionia volcano,” after the now defunct town of Ionia, Nebraska. The burning bluff was not, however, due to volcanic activity, but rather to the heat released by oxidizing minerals on the rapidly eroding river bluff.

A few weeks later, on September 14, 1804, Clark again set out to investigate a possible volcano that had been referred to in the papers of fur trader and explorer Alexander MacKay. “I walked on Shore with a view to find an old Volcano Said to be in this neghbourhood by Mr. McKey,” Clark wrote. “I was Some distance out    Could not See any Signs of a Volcanoe, I killed a Goat, which is peculier to this Countrey about the hite of a Grown Deer Shorter, its horns Coms out immediately abov its eyes.” As there is no volcanic activity in this part of South Dakota, the phenomenon observed by Mackay (and not by Clark) was likely similar to the burning lignite bluff Clark had seen earlier.

Though they did not know it, Lewis and Clark were destined to see some of the most spectacular volcanoes in North America.

On November 3, 1805, Sergeant Patrick Gass wrote in his journal:

The morning was foggy: one of the men went out and killed a fine buck. At 9 we proceeded on, but could not see the country we were passing, on account of the fog, which was very thick till noon when it disappeared, and we had a beautiful day. We at that time came to the mouth of a river on the south side, a quarter of a mile broad, but not more than 6 or 8 inches deep, running over a bar of quicksand. At this place we dined on venison and goose; and from which we can see the high point of a mountain covered with snow, in about a southeast direction from us. Our Commanding Officers are of opinion that it is Mount Hood, discovered by a Lieutenant of Vancoover, who was up this river 75 miles.

Mount Hood

Mount Hood

It was indeed Mount Hood, one of the volcanoes in the Cascade Volcanic Arc, which includes more than 20 volcanoes in present-day Canada, Washington, Oregon, and Northern California.  Formed due to one tectonic plate sliding under another on the western edge of the continent, the Cascade volcanoes are among the most potentially dangerous in the world.

Lewis and Clark’s party observed five of these, including Mount Hood, Mount Adams, Mount Rainier, Mount St. Helens, and Mount Jefferson, named by the Corps in honor of their presidential patron. The last major eruption of Mount Hood occurred in 1781-1782, but a more recent eruptive episode had occurred shortly before Lewis and Clark’s arrival in 1805. At the downstream end of the Columbia River gorge, Lewis and Clark noted the rich bottomlands that had been partially formed by Mount Hood’s eruption less than twenty-five years earlier. But they did not realize that the bottomlands had been formed by Mount Hood, an active volcano.

Nor did they know that Mount St. Helens had recently undergone a significant eruption. An explosion at Mt. St. Helens around the year 1800 probably rivaled the 1980 eruption in size, spreading ash over central and eastern Washington, northern Idaho, and western Montana.

Mount St. Helens erupting, May 1980

Mount St. Helens erupting, May 1980

Lewis and Clark did know something of what to expect geographically when they got to the Cascade Range due to the explorations of George Vancouver, though they initially mistook a newly-sighted peak, Mount Adams, for Mount St. Helens, and mistook Mount St. Helens for Mount Rainier. By the time they had made winter camp at Fort Clatsop, however, Clark had sorted out his map and assigned the right names to the right peaks. Lewis and Clark noted the conical nature of some of the mountains, but they apparently did not draw the connection that they were in the midst of a chain of volcanoes. Minor eruptions in the 19th century filled in the gaps as explorers and settlers realized they were living in the midst of potentially explosive geologic giants.

Lewis and Clark’s last near-miss with volcanic activity came in the summer of 1806, when they passed to the north of the amazing thermal features of present-day Yellowstone National Park. Yellowstone National Park is centered over the Yellowstone Caldera, the largest supervolcano on the continent. Like the Cascade volcanoes, the Yellowstone Caldera is considered an active volcano.

Boiling pots in "Colter's Hell"

Boiling pots in "Colter's Hell," Yellowstone National Park

In 1806, John Colter, a member of the Corps of Discovery, left the Lewis and Clark Expedition with Lewis’s consent to join a group of fur trappers. After splitting up with the other trappers, Colter passed through a portion of what later became Yellowstone National park during the winter of 1807–1808. He observed at least one geothermal area in the northeastern section of the park, near Tower Fall. After surviving wounds he suffered in a battle with members of the Crow and Blackfoot tribes in 1809, he gave a description of a place of “hidden fires, smoking pits, noxious steams, and smell of brimstone” that was dismissed by many people as delirium or exaggeration. Later, Colter’s observations were borne out by the reports of other mountain men who visited the area. The place he described was nicknamed “Colter’s Hell.”

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