In the Wake of the Yellowstone Hotspot

Anyone who drives through southern Idaho on Interstates 84 or 15 must endure hours and hundreds of miles of monotonous scenery: the vast, flat landscape of the Snake River Plain. In many areas, sagebrush and solidified basalt lava flows extend toward distant mountain ranges, while in other places, farmers have cultivated large expanses of volcanic soil to grow Idaho’s famous potatoes. Southern Idaho’s topography was not always so dull. Mountain ranges once ran through the region. Thanks to the Yellowstone hotspot, however, the pre-existing scenery was destroyed by several dozen of the largest kind of volcanic eruption on Earth—eruptions that formed gigantic craters, known as calderas, measuring a few tens of miles wide. Some 16.5 million years ago, the hotspot was beneath the area where Oregon, Nevada, and Idaho meet. It produced its first big caldera-forming eruptions there. As the North American plate of Earth’s surface drifted southwest over the hotspot, about 100 giant eruptions punched through the drifting plate, forming a chain of giant calderas stretching almost coo miles from the Oregon—Nevada—Idaho border, northeast across Idaho to Yellowstone National Park in northwest Wyoming. Yellowstone has been perched atop the hotspot for the past 2 million years, and a 45-by-30-mile-wide caldera now forms the heart of the national park. After the ancient landscape of southern and eastern Idaho was obliterated by the eruptions, the swath of calderas in the hotspot’s wake formed the eastern two-thirds of the vast, 50-mile-wide valley now known as the Snake River Plain. The calderas eventually were buried by basalt lava flows and sediments from the Snake River and its tributaries, concealing the incredibly violent volcanic history of the Yellowstone hotspot. Yet we now know that the hotspot created much of the flat expanse of the Snake River Plain. Like a boat speeding through water and creating an arc-shaped wave in its wake, the hotspot also left in its wake a parabola-shaped pattern of high mountains and earthquake activity flanking both sides of the Snake River Plain.

Yellowstone Tour

This tour of Yellowstone National Park and the Hebgen Lake earthquake area begins at Yellowstone’s south entrance, just north of Grand Teton National Park. Those entering Yellowstone from other directions may start this tour at any stop that is convenient. For that reason, we have not shown cumulative mileage for this trip from start to finish. Instead, we provide cumulative mileage only from one stop to the next, and for points of interest between them. (Figure 9.1. See also Figure 1.4 for a view of the region’s topography.) Two long days or three less hectic days are required for this 251-mile tour. For those with limited time, some time-saving options are included, such as skipping West Yellowstone, Montana, and the Hebgen Lake earthquake area (Stops 7—12) or omitting Mammoth Hot Springs and other stops on the northern end of the park (Stops 14—16). If you want to spend only two days in Yellowstone and its environs, start early the first day (136 miles) and continue to Stop 12, West Yellowstone, Montana, where overnight accommodations are available. During the second day, visit Stops 13—20 (115 miles). If you wish to divide this chapter’s tour into three days, begin at Stop 1 and proceed through Stop 7, also West Yellowstone (79 miles). Spend the night there. Tour the Hebgen Lake area, Stops 8—11, the second day and return to West Yellowstone, Stop 12, the second night (57 miles). Cover Stops 13—20 the third day (115 miles). The tour ends inside Yellowstone, so you may want to spend the night in the area if you have a long drive home. The driving tour of Yellowstone is passable only from late spring to fall, when park roads are open. West Yellowstone, Montana, and the Hebgen Lake area, Stops 7—12, are accessible year-round, although winter snow covers most geological features. Vehicle odometers vary, sometimes significantly, so mileages should be taken as approximate. Some visitors may choose to drive part or all of these tours in a direction opposite to the one we use.

Future Disasters

In 1870, the fall before Ferdinand Hayden’s celebrated exploration of Yellowstone, an Army lieutenant named Gustavus C. Doane guided a small troop into the mysterious high country. Unlike Hayden, Doane did not conduct extensive scientific studies. However, Doane was observant. He said of Yellowstone: . . . As a country for sight seers, it is without parallel. As a field for scientific research it promises great results, in the branches of Geology, Mineralogy, Botany, Zoology, and Ornithology. It is probably the greatest laboratory that nature furnishes on the surface of the globe. . . . Yellowstone’s value as a unique ecological region soon gained recognition when in 1872, it was designated as the first national park in the United States—and in the world. The complex relationships among Yellowstone’s fauna, flora, and geology helped inspire America’s budding conservation ethic, which came to fruition only a century later with widespread recognition of the tenuous interdependence of living organisms and the Earth they occupy. The idea of a greater Yellowstone ecosystem recognized that its living and geological wonders extended beyond the park’s boundaries and into a broader area. The greater Yellowstone ecosystem is defined by the subterranean yet dominant presence of the Yellowstone hotspot, the engine that ultimately drives not only the region’s geology, but also its living organisms. The Rocky Mountains, lifted upward tens of millions of years ago, were pushed perhaps 1,700 feet higher at Yellowstone during the past 2 million years by the upward-bulging hotspot. Today, a line drawn at 6,100 feet elevation roughly demarcates the boundaries of the greater Yellowstone ecosystem. The high altitude is critical in creating the temperature and moisture regimes that gave rise to Yellowstone’s biological wonders and now determine the distribution of its plants and wildlife. In addition, the incredible amount of heat rising from the hotspot is responsible for Yellowstone’s history of volcanism and its geysers and hot springs, rich with exotic microbes that branched off the evolutionary tree at a primitive stage of life on Earth. Yelllowstone’s expansive lodgepole pine forests demonstrate the interaction of the park’s biology and geology. They grow well on rhyolite lava flows that cover most of western and central Yellowstone.

The Broken Earth: Why the Tetons Are Grand

On a summer morning when the breeze blows cool, it is easy to re the lakes and sagebrush-covered glacial plains of Wyoming’s Jackson Hole sit at nearly 7,000 feet elevation. Yet the altitude of this gorgeous valley is diminished by the view to the west: The precipitous east front of the Teton Range towers above the valley floor, with 13,770-foot Grand Teton and other rugged, snowclad peaks catching the first golden rays of daybreak. This is one of the most spectacular mountain vistas in America. Whether at chill dawn, in glistening light after a torrential afternoon thunderstorm, or during summer evenings when the sun descends behind the lagged Tetons, it is a view that brings solace and peace. Yet the serene splendor of Grand Teton National Park belies a hidden fury. It is not volcanism, which is concealed beneath the gentle pine-covered Yellowstone Plateau to the north. Instead, this defiant topography was born of seismic disaster as the Teton fault repeatedly and violently broke the earth, producing a few thousand magnitude-7 to -7.5 earthquakes during the past 13 million years. During each major jolt, Jackson Hole dropped downward and the Teton Range rose upward, increasing the vertical distance between the valley and the mountains by 3 to 6 feet and sometimes more. Now, after 13 million years of earthquakes, the tallest peaks tower almost 7,000 feet above the valley floor. Actual movement on the fault has been even greater. Jackson Hole dropped downward perhaps 16,000 feet during all those earthquakes. Rock eroded from the Teton Range and other mountains by streams and glaciers filled Jackson Hole with thousands of feet of sediment, disguising how much the valley sank. Combine the uplift of the mountains and the sinking of Jackson Hole, and the best estimate—although still plagued by uncertainty—is that movement on the Teton fault has totaled 23,000 feet during the past 13 million years. That is a tiny fraction of Earth’s 4.6-billion-year history. Consider the effects of repeated episodes of mountain-building during eons before the Teton fault was born: The oldest rocks high in the Teton Range are 2.8-billion-year-old gneisses and schists and 2.4-billion-year-old granites.

Cataclysm!: The Hotspot Reaches Yellowstone

Epicenters from numerous earthquakes fall approximately along two parallel lines that stretch from southeast to northwest through Yellowstone National Park. During the past 630,000 years, lava flowed from eruptive vents located roughly along the same lines. The alignment of earthquakes and small volcanoes suggests that zones of weakness are deep beneath them within the Earth. Those zones may be the still-active roots of faults that once ran along the base of towering mountains. Such mountains would have made ancient Yellowstone resemble today’s Grand Teton National Park. Indeed, a few million years ago these mountains may have stretched northward through Yellowstone and hooked up with the Gallatin Range, which now extends from Montana south into Yellowstone’s northwest corner. So why is today’s Yellowstone Plateau relatively flat? What happened to the mountains that once may have rose thousands of feet skyward like the Tetons do today? The answer, quite simply, is that they were destroyed 2 million years ago during a caldera eruption, which is the largest, most catastrophic kind of volcanic outburst—an explosion so cataclysmic that it dwarfs any eruption in historic time. North America had continued its southwestward slide over the Yellowstone hotspot. After blasting and repaving the Snake River Plain, the hotspot was finally beneath the place for which it later was named. The power of its rising heat and hot rock began to shape Yellowstone into what it is today. The first eruptive blast at Yellowstone 2 million years ago left a gigantic hole in the ground—a hole larger than the state of Rhode Island. The huge crater, known as a caldera, measured about 5o miles long, 40 miles wide, and hundreds of yards deep. It extended from Island Park in Idaho to the central part of Yellowstone in Wyoming. During the volcanic cataclysm, hot ash and rock blew into the heavens over Yellowstone, then rained like hell from the sky. As heavier pumice and ash particles debris piled up on the ground, their heat welded the debris together to form a layer of solid rock called ash-flow tuff or welded tuff.

Ice over Fire: Glaciers Carve the Landscape

Yellowstone, the Tetons, and Jackson Hole were shaped by multiple catastrophes. Huge volcanic eruptions and powerful earthquakes played major roles. Finishing touches were added by another kind of calamity: A rare global Ice Age produced gigantic glaciers that buried the landscape with ice two-thirds of a mile thick in places. The glaciers carved mountains, canyons, and lake basins. They dumped large piles of debris and redirected the flow of rivers. The Yellowstone—Teton region is a world-class example of how land was reshaped by glaciers during what is known as the Pleistocene Ice Age. The Ice Age was not a single glacial period, but many intermittent cold spells interspersed with warmer periods during which the ice melted. The timing of major glacial periods is notoriously uncertain. Although continental ice sheets did not quite reach as far south as Yellowstone, a regional icecap and large glaciers covered the Yellowstone—Teton country during three major episodes of at least the past 300,000 years—and perhaps the past 2 million years. The last of these big glaciers retreated about 14,000 years ago, although some argue they did not recede until 10,000 to 12,000 years ago. Today, small glaciers in the Teton Range are found only above 10,000 feet. During each major episode, most of Yellowstone National Park was buried beneath an icecap as much as 3,500 feet thick, among the largest in the ancient Rocky Mountains. Gigantic masses of ice flowed down from the high Yellowstone Plateau, carving and scouring the Earth’s surface, diverting and damming rivers into their present forms, steepening mountain fronts, and deepening lakes. The ice helped sculpt the Grand Canyon of the Yellowstone. More than anything, the thick ice scraped Yellowstone’s volcanic topography, further smoothing the plateau and helping to excavate the basin occupied by Yellowstone Lake. Jackson Hole became a rendezvous of glaciers converging from the north, north-east, and west. Ice up to 2,000 feet thick scooped out the valley floor. The glaciers left tall ridges of rocky debris now covered by lush conifer forests. Such ridges, called moraines, helped shape Jackson Lake.

Grand Teton Tour

Because winter snows close roads in both Grand Teton and Yellowstone national parks, the driving tours in this chapter and the next are intended for use only from late spring through early fall. You may wish to do only parts of each tour and so we have not shown cumulative trip mileage in these tour guides. Instead, we provide cumulative mileage only from one stop to the next, and for points of interest between them. This chapter’s tour of Grand Teton National Park totals 82 miles, excluding mileage to the optional aerial tramway ride. The intent of these two chapters is to provide a three-day driving tour, including one day in Grand Teton and two in Yellowstone. However, you easily may extend the tour to five days or even longer if you choose a leisurely pace or decide to make optional hikes and stops. The three-day tour outlined in these chapters starts in the town of Jackson, Wyoming. Our tour includes the following suggestions: • On day I, make the Teton tour, perhaps beginning or ending with the optional tramway ride detailed at the end of this chapter. Spend the night either in Jackson or find accommodations closer to Yellowstone, such as at Colter Bay Village or other campgrounds and lodgings in northern Grand Teton National Park. • On day 2, enter Yellowstone’s south entrance and drive the loop road clockwise to Madison Junction, then spend the night at West Yellowstone, Montana. If you arrive at West Yellowstone by early to mid-afternoon, you still will have time to make the optional tour to the Hebgen Lake earthquake area, although the visitor center there closes in the late afternoon. • On day 3, either start with the optional side trip to the Hebgen Lake earthquake area, or proceed from West Yellowstone, Montana, back into Yellowstone National Park, continuing the tour at Madison Junction. Some visitors may choose to drive part or all of these tours in a direction opposite to the one we use here. For that reason, we also provide reverse mileage between each stop and the sights between stops.

How Yellowstone Works

Most people who visit Yellowstone are blissfully unaware they are standing on top of an active, breathing volcano. They visit geysers and hot springs, and may feel some of the numerous earthquakes that rattle the region. Few realize the seemingly solid ground beneath them is slowly stretching apart and huffing and puffing upward and downward. Nor are many visitors aware of the large chamber of molten and partially molten rock several miles beneath their feet, or of the even deeper plume of hot rock moving up from deep within Earth. Indeed, it is easy to enjoy the national park’s geysers and other scenery without stopping to consider they are merely the uppermost, most visible parts of one of the world’s geological wonders: the Yellowstone hotspot. Even fewer tourists realize the same forces driving Yellowstone’s renowned geysers also reshaped the landscape of 25 percent of the northwestern United States—a broad band stretching from Yellowstone almost 500 miles southwest to the Idaho—Oregon—Nevada border. As North America drifted southwest over the hotspot during the past 16.5 million years, the immense heat and molten rock rising from Earth’s mantle melted, rearranged, and blew apart the overlying crust. Today, the hotspot is beneath Yellowstone, making the national park a field laboratory of active geologic process: volcanism, earthquakes, faulting, and large-scale movement and deformation of Earth’s crust. Let us examine how this system works—how heat and magma, or molten rock, from within the Earth drive small-scale features such as geysers and hot springs, contribute to the most intense earthquake and volcanic activity in the Rocky Mountains, and help mold the topography of the region. The amount of heat flowing from the ground in the Yellowstone caldera is thirty to forty times more than the heat emitted by an average piece of ground elsewhere on Earth’s continents. This enormous heat flow provides the energy that melted rock under the caldera and helped lift Yellowstone to its lofty altitude. Heat powers Yellowstone’s volcanic activity by melting rock in Earth’s mantle and crust. In turn, the molten rock heats groundwater to produce geysers and hot springs.

A Land of Scenery and Violence

It was the busy summer season in Yellowstone National Park, a beautiful moonlit night with 18,000 people in the park’s campgrounds and hotels and thousands more in surrounding towns and recreation areas. At 23 minutes before midnight, a talent contest was wrapping up at the Old Faithful recreation hall. A beauty queen had just been crowned. As she walked down the aisle to the applause of several hundred people, the log building creaked loudly and began to shake. Within seconds, the earthquake sent people scurrying for the exits. A park ranger dropped the hand of his date—a waitress from Old Faithful Inn—and rushed to open the doors so no one would be trampled. Nearby, frightened guests fled Old Faithful Inn, where a waterline broke and an old stone chimney soon would collapse into a dining room, thankfully closed at that late hour. Out in the darkness, in geyser basins along Yellowstone’s Firehole River, the Earth began belching larger-than-usual volumes of hot water. About 160 geysers erupted, some for the first time, others after decades-long dormant periods. Sapphire Pool, once a gentle spring, became a violent geyser, hurling mineral deposits around Biscuit Basin. Clepsydra, Fountain, and some other geysers in Lower Geyser Basin began erupting more often than usual. Old Faithful’s eruptions became less frequent, although some observers thought it spouted with unusual vigor earlier that evening. Hundreds of hot springs became muddy. Fountain Paint Pot spewed mud violently, spattering tourist walkways. Rocks and landslides tumbled into park highways in several places, blocking roads between Old Faithful and Mammoth and closing the route to the park’s west entrance at West Yellowstone, Montana. Within an hour, thousands of vehicles streamed out of Yellowstone on roads that remained open—a serpentine parade of headlights fleeing the strongest earthquake yet recorded in the Rocky Mountains and the Intermountain West. The panic and damage in Yellowstone were minimal compared with the unimaginable horror that would overtake a popular Montana recreation area just outside the park’s northwest boundary.