Mendenhall Glacier & Ice Cave FAQs

Why do glaciers form?

In Southeast Alaska, maritime climate and coastal mountains create favorable conditions for glaciation. Moist air flows toward the mountains, rises and releases snow and rain. Average annual snowfall on the Juneau Icefield exceeds 100 feet. Mild Southeast Alaskan summers cause winter snow accumulation to exceed summer snowmelt at higher elevations. Year after year, snow accumulates, compacting underlying snow layers from previous years into solid ice. Mendenhall Glacier is one of the 38 large glaciers that flow from the 1500 square mile expanse of rock, snow and ice known as the Juneau Icefield. As glacial ice continues to build, gravity pulls the ice down slope. The glacier slowly scours the bedrock and grinds down its 13-mile journey to Mendenhall Lake.

Is the glacier retreating?

A neo-glaciation period began 3,000 years ago and ended in the mid-1700s. At this time, Mendenhall Glacier reached its point on maximum advance, and its terminus rested almost 2.5 miles down valley from its present position. Mendenhall Glacier started retreating in the mid-1700s because its annual rate of melt began to exceed its annual total accumulation. The icefield's snowfall perpetually creates new glacial ice for Mendenhall Glacier and this ice takes 200-250 years to travel from the Juneau Icefield to Mendenhall Lake. Water depth at the glacier's terminus is 220 feet. At this rate, the glacier would take several centuries to completely disappear. For Mendenhall Glacier to advance, the icefield's snowfall needs to increase, the glacier's rate of melt needs to decrease, or both.

What happens after the glacier retreats?

As Mendenhall Glacier retreats and uncovers bare rock, the wind carries seeds and spores of moss onto barren land. Alder, willow and cottonwood tree seeds systematically grow in degalciated landscapes. Glacier debris, poor in nutrients, depends on flowering lupine and alder to fix nitrogen in the soil, and all species add organic matter to the soil as they are overtopped and shaded out by other species. Spruce and hemlock ultimately rise to close the forest canopy, eventually creating an old growth forest. Encompassing almost 350 years, this sequence of plant succession provides habitat for an increasing number of plants and animal species.

What evidence do glaciers leave behind?

The base of Mendenhall Glacier works like a giant piece of sandpaper. As the ice flows towards Mendenhall Lake, the glacier plucks rocks that become imbedded in the ice from the valley floor. The glacier scrapes these rocks across the bedrock creating grooves and striations. The glacier's erosive power changes the landscape and scrapes much of the soil and rock from the valley walls. Rocks scoured from the surrounding valley wallscan fall on to the glacier and be transported down valley. This process can create dark debris lines called moraines on the edges and, where two branches come together, down the center of the glacier. As the glacier continues its path towards Mendenhall Lake, it carries debris like a conveyor belt and deposits it in the lake. As it moves the glacier also grinds up rock to a fine powder called rock flour that escapes with glacial melt water and creates the lake's murky color. 

What wildlife lives near the glacier?

Coyote, porcupine, squirrel, snowshoe hare, and short-tailed weasel build homes on the valley floor, and migrating songbirds build nests in the deciduous shrubs in the young forest. In Steep Creek, beavers work to create ponds while spawning sockeye and coho salmom provide a food source for black bears and eagles. Loons, gull and Arctic terns nest around Mendenhall Lake, and mountain goats favor the rocky terrain and alpine meadows on the surrounding peaks.

I heard there is an ice cave at Mendenhall Glacier. Where is it?

There are several ice caves, but the cave that appears in most photos is quite challenging to access. It is located along the west flank of the glacier.

How can I prepare for a trip to the ice cave?

A trip to the western ice cave, while inspiring, is also dangerous.  If you choose to go to the cave, be aware of the risks and go prepared and with a guide. 

  • Allow at least six to eight hours for a trek to the cave. Many people underestimate the time required and as a result they wind up lost and out of daylight.
  • Dress in layers and bring extra clothing. A day that starts warm can turn cold and rainy. Bring extra clothing in case a change of dry clothes is needed or you get lost and spend the night outdoors. Hypothermia is a valid concern.
  • Wear sturdy footwear such as hiking boots. Both the rocks and the glacier can be slippery. Loose soil and rocks are regularly encountered. Glacier travel requires crampons, ice axe and rescue gear, and the skills to use them.
  • The ice cave may collapse either in whole or in part, injuring or killing people and pets inside or on top of the cave. The cave entrance is thinner and more vulnerable to collapse. Rocks atop the entrance can fall unseen. People have been killed and injured in ice cave collapses on Mt. Baker and on Mt. Hood. 
  •  Do you have the skills to travel on a glacier? Crevasses can be hidden by a thin bridge of snow. Slopes near moulins (holes) can be slippery. The glacier can calve and shift at any time.
  • Have a communication plan. Let someone you trust know what route you plan to take and when you plan to return. They can call for help if you don’t return on time.
  • Since there are no accurate route maps, track your progress with GPS in order to find your way back. Cell service may or may not be available. While many people find their way to the glacier, many get lost when returning from the cave as the trail is not obvious. Lost hikers who try to find their way to the lake’s edge often find themselves at a cliff. You want to be one of those who make it back without the need for rescue. Bring enough food and water to survive an unplanned overnight stay.

How do I get to the ice cave?

There are two general routes people take to the ice caves: over land and over the lake. Both routes involve hazards not normally found on trails and it is strongly recommended to go with someone who knows the route.

The lake route involves paddling a water craft on an icy-cold lake and passing near the glacier face where large bergs may break off at any time. This should only be attempted by those with cold-water paddling skills including an ability to self-rescue in the event of capsize.  Strong, cold, downslope winds can cause 1-2’ choppy waves on the lake, particularly on warmer, sunny days.  Waves from glacial calvings (collapse of the glacial terminus face) can cause watercraft to capsize or wash watercraft off the shoreline. Birds nest near the landing beach and should not be approached within 250 yards (2 ½ football fields). This route also requires foot travel for 30 minutes along the glacier edge where rock is especially loose, or on the glacier itself with the hazards of crevasses and slippery ice.

Many people use an overland route that begins at the West Glacier trail and veers onto an unmaintained, unofficial path through the forest and across a moon-scape of loose rock with a confusing array of markers.  The overall route length to the caves is approximately 4 miles one-way and the majority of it is over rough, steep, uneven, unmarked, and slippery terrain. Pay careful attention as you proceed in order to return on the same route, or better yet, follow a GPS course. Many people get lost on the return from the ice cave. Slips and falls down steep and sometimes wet rock faces are all too common.

Nesting birds: gulls and arctic terns nest on the rock peninsula. Recreationists can easily step on and kill an egg or nestling. Stay 250 yards away from nesting areas and roosting birds. The presence of people and especially dogs can negatively affect nesting success.

What do I need to be aware of if I go in the winter on the frozen lake?

Areas of particular concern in the winter route are:

  • Lake ice is never safe. The thickness is not measured or monitored by the Forest Service. Lake ice can vary in thickness due to water flowing into the lake.
  • Ice is thinner at the mouth of Steep Creek, near Nugget Falls, and near any running water.
  • Icebergs can roll over without warning, even when the lake is frozen. When Icebergs roll, they break up the lake ice around them.
  • The face of the glacier is an active calving zone at all times of the year. In the winter, a calving can shatter the lake ice.  Ice near the face of the glacier is also weaker due to calving and the movement of the glacier. Most reports of people falling through the ice come from the face of the glacier.
  • Rockslides can and do break up lake ice.

Why is the ice blue?

Glacial ice appears blue because it absorbs all colors of the visible light spectrum except blue, which it transmits. The transmission of this blue wavelength gives glacial ice its blue appearance. Glacier ice may also appear white because some ice is highly fractured with air pockets and indiscriminately scatters the visible light spectrum.

Who was Mendenhall?

Appointed by President Harrison, Thomas Corwin Mendenhall (1841-1924) served as Superintendent of the U.S. Coast and Geodetic Survey from 1889 to 1894. A noted scientist, Mendenhall also served on the Alaska Boundary Commission that was responsible for surveying the international boundary between Canada and Alaska. In 1892, this glacier was renamed to honor Mendenhall. Naturalist John Muir first named the glacier Auke Glacier in 1879 after the Aak'w Kwaan of the Tlingít Indians.