GRINNELL GLACIER, Mont. — National Park Service Ranger Jude Chauvette led 40 hikers single file slowly across this mile-wide glacier, dodging deep crevasses of powder-blue ice.
The glacier was not a quiet place.
Rocks tumbled from towering, knife-edged Garden Wall, a soaring jagged cliff that is gradually being devoured by 6,400-foot-high Grinnell Glacier.
The pressure exerted by the 700-foot-deep block of ice at the base of Garden Wall causes the rock-ribbed mountain to crumble continuously.
At the other end of the half-mile-long glacier, chunks of ice fell into milky Upper Grinnell Lake, becoming icebergs. Nearby a thundering waterfall spilled down Garden Wall. Rivulets of rushing ice water crisscrossed the rock-strewn glacial surface.
There were rumblings from below as the glacier settled in.
As the hikers followed Chauvette onto the glacier, the ranger warned: "Walk single file. Watch out for crevasses. Walk on ice, not snow, so as not to fall into one of the deep frozen fissures.
"In all the many years of hiking on this glacier we have never had anyone fall into a crevasse yet," said Chauvette, 27, a seasonal ranger who during the school year teaches high school biology in Nashua, N.H.
"We don't want to spoil that record today," he said. "It can happen. A skier was killed not long ago when he skied into a crevasse on Sperry Glacier in Glacier National Park."
Nearby was a rescue cache filled with ice axes, ropes and crampons to be used in the event a hiker slipped into one of the cracks.
Carefully avoided were certain sections of the glacier, such as the Brutal Zone, where fissures fan out in all directions, and ice caves near the edge can collapse at any time.
Each summer about 2,000 hikers make the daylong trip, the only regular ranger-led hike on a glacier in the continental United States. The journey is four or 5 1/2 miles in each direction, depending on which route is taken up the steep trail from Many Glacier Lodge in northwest Montana, 30 miles south of the U.S.-Canadian border.
The trail is snowed in and impossible to climb except for seven or eight weeks in July and August. This year the trail opened July 7 and group hikes end today. Spring, summer and fall are short-lived in the high reaches of this million-acre Rocky Mountain national park dotted with 60 glaciers. The alpine hills are ablaze with a rainbow of wildflowers that grow, bloom and then prepare for winter all within a span of two months.
As the hike began, Chauvette cautioned: "There is safety in numbers. This is grizzly country. Huckleberry bushes are full and grizzly bears are feasting on them. By making noises the grizzly are alerted to your presence."
Don't Scare a Grizzly
Many hikers carry bear bells purchased at Many Glacier Lodge. Chauvette said it isn't a bad idea to ring the bells every so often to help keep the grizzly away.
"The problems (occur) when the bear doesn't know people are out there and people don't know the bear is close by. When they meet, both are scared. You don't want to scare a grizzly bear. A scared grizzly is a very dangerous bear, indeed."
Only one grizzly was spotted at a distance, but a herd of mountain goats and a couple dozen bighorn sheep were encountered close up as the group hiked to the glacier.
The hikers on this particular day came from many parts of the country including Gillette, N.J., Middletown, Conn., Chadds Ford, Pa., Minnesota, Illinois, Indiana, South Carolina and Washington. From California were Libby and Ken Perrin, 50, of Malibu. Ken Perrin chairs the natural-science department at Pepperdine University.
Ranger Chauvette noted that one-third of the Earth's land was once covered by glaciers, and that Grinnell Glacier is estimated to be 4,000 years old. "Grinnell, like all glaciers, is ever moving, ever changing," said Chauvette, who makes the hike three times a week. "Grinnell moves 35 feet a year. Patterns of the crevasses are always different."
Measuring the Drift
Scientists have spent summers on the the glacier for the past 100 years, beginning with its discovery by George Bird Grinnell in 1887.
"Very few glaciers are this accessible. That's why glaciologists are up here every year with sophisticated instrumentation," Chauvette explained.
Scientists from the U.S. Geological Survey and University of Washington use huge numbered rocks to measure drift, speed, direction and movement of the glacier. Photographs are taken to detect changes in thickness and water runoff. Rainfall and snowfall records are kept to detect melt.
Grinnell Glacier is slowly shrinking; it is half as big as it was in the late 1880s, according to records.
Two million people visit Glacier National Park each summer, but only about 2,000 participate in the ranger-led hikes to the glacier, Chauvette said.
"Fewer than 5% of them ever get out of their car for any length of time," he said. "They just drive through."