Into the steam caves

An early National Park Service photo showing climbers inside the steam caves

Lacking blankets for a bivouac or sunlight for a descent, they huddled in the eerie cavern for its wind shelter and relative warmth--though at just above freezing, they must have had one long, cold bummer of a night.

A few climbers since then have used the firn-snow caves for an emergency shelter. A few more have probably even ducked into the upper part of a cavern for some quality time in a makeshift outhouse. But after completing the grueling hike to the summit, few venture more than a quick glance into the icy, dark holes. As a result, not many know much about the caves--or even that they're there.

In 1970--exactly 100 years after Stevens and Van Trump huddled for life--Drs. Eugene Kiver and Martin Mumma, of Eastern Washington State College, made the first complete scientific examinations of the caves.

Camping at the summit they explored and mapped the caverns with a tripod-mounted compass and measuring tape. Inside they found a main perimeter passage running parallel in an arc to the outer rims of each crater some 50-70 meters from the surface. Numerous exhaust passageways run perpendicular to the perimeter tunnel, up the crater slope to the rim.

The ground in the craters is mostly loose, igneous rubble, with some rocks as large as two meters across. Fumaroles--holes in the ground that exhaust the volcano's heat--are the engine that drives the melting process.

The walls and ceiling are firn snow--the same age-hardened ice that comprises glaciers. This ice cycles like a glacier, accumulating on the surface and ablating (or, in English, melting) down lower.

Instead of melting as it slides to a lower, warmer elevation like a glacier, ablation on the summit comes as the mountain's heat melts the underside of the ice plug. The majority of this melted water escapes into the crater and finds its way down the mountain as groundwater.

The caves hid plenty of surprises for the explorers, however. Two passages led to large rooms. One room, over a hundred feet across, held a large reservoir of melt-water--in effect, a lake at the summit of Mount Rainier.

Another large room, this one dry, contained debris left on the summit that had subsided--that is, sunk through the firn snow through its accumulate-melt cycle --and fallen into the room. Among this included 50-year-old cans and wool gloves. They named it "the bird room" for the skeletal remains of long dead birds, fallen at the summit.

In general, the caves are extremely stable. Slight variation in width and shape occurs from season to season, but on an annual basis the snowpack and heat are in remarkable equilibrium. According to Kiver, an upset in this balance would be one means of predicting future activity of the volcano.