$Unique_ID{bob00999} $Pretitle{} $Title{Glacier Bay Galloping, Calving, Advancing, Retreating} $Subtitle{} $Author{Kirk, Ruth} $Affiliation{National Park Service;U.S. Department Of The Interior} $Subject{ice glacier glaciers water hopkins johns inlet bergs advancing feet see pictures see figures } $Date{1983} $Log{See Fairweather Range*0099901.scf } Title: Glacier Bay Book: Part II: Of Time And Ice Author: Kirk, Ruth Affiliation: National Park Service;U.S. Department Of The Interior Date: 1983 Galloping, Calving, Advancing, Retreating Johns Hopkins All morning we have been charting in upper Johns Hopkins Inlet. The high peaks of the Fairweather Range thrust like white fangs above us. Beside us rise gray, bare, abrupt rock walls. We arrived here aboard Growler about 2100 last evening. Sunlight still flooded the upper walls but the water already stood in twilight, lending an eerie quality to this cathedral-like fjord. Eager to see whether the Tyeen Glacier had surged forward since last summer, we barely noticed, however. Austin, Dave, Emily, Charles, and I all crowded into the wheelhouse, with last year's aerial photograph on the chart table for comparison with what we hoped to see ahead, a glacier that galloped. Alas, no drama greeted us. The ice still hung near the top of the cliff, poised to surge, perhaps, but far from having done so. [See Fairweather Range: Climbers find the Fairweather Range, with its quixotic and severe weather, misnamed. This immense land seems to triple in size immediately when you get in a tight spot.] Two hundred galloping glaciers are known in Alaska and northwestern Canada, some occasionally surging several kilometers in a single year. These extraordinary advances occur only on certain glaciers. No glaciers overlying granitic bedrock are given to surging. Many that do surge are associated with geologic faults, but not all. Water beneath the ice has been advanced as an explanation for galloping glaciers, but this can't be the whole answer. A mountain glacier is usually rushing if it moves a meter or two (4 to 7 feet) a day. Deformation permits the ice to bend and slide around obstacles, and the enormous pressure against any such protrusion produces enough heat to melt a fraction of the glacier's undersurface. Lubricated by this minute film of meltwater, the ice jerks forward. That relieves the pressure and the melt-film refreezes. The process starts anew. I once watched this happen where University of Washington researchers had dug a 25-meter (85-foot) tunnel to bedrock beneath the Blue Glacier in Washington's Olympic Mountains. Gauges imbedded in the tunnel walls measured the pressure the ice exerted against irregularities in its bed and the rate of its jerky flow over and around them. Dials dispassionately registered what was happening, but you could see it without them. A knob of bedrock might have ice pressed against it. Then a momentary wetness would darken the rock and an additional fraction of the knob would be engulfed. The process was silent and, but for the glaciologists' lights, would haven taken place in utter blackness. Water beneath ice may not fully explain why some glaciers gallop, but meltwater - with land runoff - surely affects the rate at which Glacier Bay's glaciers perform their greatest scenic wonder: calving icebergs off their tidewater snouts. The water works down through the ice and momentarily lifts the glacier off bedrock during brief periods of exceptional hydrostatic pressure. The lifting weakens the ice and accelerates collapse. Some feel that low tide may also step up calving. Ice in contact with saltwater melts more rapidly than ice exposed only to air, producing undercutting - and reduced support - at the high-tide line. Others find this erosive undercutting inconsequential to calving. Geological Survey monitoring establishes no relation between tide and calving rate. Icebergs themselves are far from uniform. Those that look white hold myriad trapped air bubbles. Blue means denser ice. Greenish-black ice is from the bottom, or sole, of a glacier and such bergs may also be grooved where bedrock knobs have gouged the glacier. Morainal rubble stripes some icebergs with brown, or totally darkens them. Rocks ride atop bergs and plop into the water from their sides. Stranding icebergs leave tracks as they half float, half drag along the beach. And they grind, squash, and rip seaweeds and mussels pioneering rocky shores. Floating bergs offer perches favored by bald eagles, cormorants, and gulls. For eagles the bergs seem to serve as movable vantage points for spotting opportunities to prey or scavenge. Cormorants often hold out their wings to dry while they ride. Most gulls just rest. Kittiwakes - gulls that come ashore only to nest - briefly ride Glacier Bay icebergs during their August transition from nesting colonies to life at sea. Guillemots and puffins never ride the bergs, perhaps because of difficulties landing on ice. Their legs, set far back and fine for swimming, are awkward out of water. Land birds, except for eagles, generally ignore icebergs. As you kayak among bergs, paddling silently, you hear melt take its toll. Water drops and cascades. Air bubbles pop and ice cracks constantly as it adjusts to changing pressures and temperatures. Even with your eyes closed, you can tell icebergs are close. How high bergs float depends on their size and ice density and on the density of the water. Where runoff or rainwater floats atop saltwater, bergs sink lower than if freshwater is absent. The burden of rock and sediment in the ice sometimes weighs a small berg below the surface. A faint shadowy presence is all that gives it away. Huge bergs, recognizable by distinctive shape or patterning, may last a week or more, though they split or turn over as reshaping melt affects balance. What had seemed a modest floating crag may, when rolling over, suddenly loom as an enormous hazard if you've paddled too near. Studying a beached iceberg reveals its fabric and susceptibility to melt. Ice crystals that measure a centimeter (0.4 inches) or more across interlock as in a three-dimensional puzzle. Along such interfaces sun warmth and saltwater attack. Grasp a projection and wiggle it. You will hear a squeaking as the crystals rub one another along these junctions. Last evening Dave stood near Growler's bow as we approached the upper end of Johns Hopkins Inlet. Net in hand, he scooped up icebergs for the refrigerator. We had run close to the Johns Hopkins and Gilman glacier faces to take bottom readings. For these, Austin used Bergy-bit, the little radio-controlled boat which amounts to a sleek hull fitted with a tight lid. Only its three-horsepower electric motor projects vulnerably. We placed one of Growler's depth sounders inside Bergy-bit. Mid channel approaching the Johns Hopkins snout, Growler consistently recorded a water depth of 400 meters (1,300 feet) and a flat bottom, the sort of uniform contour expected of fine-grained sediments deposited in deep water. The water is so deep that there is no anchorage in this inlet. The bottom lies far beyond an anchor's reach even along the sidewalls. To our surprise, however, about one kilometer (1.5 miles) from the glacier face we measured water "only" 150 meters (500 feet) deep. The glacier is pushing a steep-sided submarine plug far out ahead of its front. Austin has found nothing like this elsewhere. We sent Bergy-bit along the east side of the Johns Hopkins ice front, and the entire front of the Gilman Glacier, and then, barely before midnight, quit for dinner. For the past two hours I had supposed we would stop, so I kept spinach noodles hot on the stove, and they turned into a startling green goo. Rather than admit culinary defeat I topped the mass with Parmesan cheese and croutons and baked it. Camaraderie and hunger sufficed to prompt praise for my baked goo. By the time we finished dinner it was technically already morning. We drifted all night. With the water too deep for anchorage, we had to depend on pack ice to hold us safely away from the fjord wall. We took turns standing watch, a long boat hook in hand for pushing off bergs that might cause trouble. At one point Emily roused Austin to start the engine and work free of encircling ice that brought with it an iceberg towering higher than Growlers rail. Mostly it was a night of ethereal peace. There was no moon but the floating ice reflected enough light so that on watch you could make out closeby bergs and the seals circling us like dark phantoms. Occasionally a seal would signal the sudden end of its curiosity and slap the water with its hind flippers, then dive. Otherwise, the only sounds were a faint roar from distant waterfalls, the sporadic grinding of ice against Growler's hull, and once the splash of an iceberg rolling over. This morning we resumed readings with Bergy-bit. I sit out of the way atop the wheelhouse while Dave controls the skiff with the radio transmitter and Emily watches with binoculars, telling him which way to turn so as to steer Bergy through leads in the ice pack. Falling ice strikes the little boat with a loud clonk and for a while Berg vanishes from sight amid a welter of falling and surging bergs. Then we see the dot of its brilliant red hull and know it has survived. Bottom readings are clear. They show a depth of 350 meters (1,100 feet) close to the west side of the Johns Hopkins ice front. We have just charted an underwater canyon. The Johns Hopkins Glacier started advancing more than 50 years ago. South of here the Brady Glacier extends a full 70 kilometers (43 miles) through the Fairweather Range to Taylor Bay. Indeed, the Reid Glacier and the Lamplugh, near the mouth of this inlet, are lobes of the Brady. It is an ice mass today choking a fjord, much as ice a few centuries ago sealed the Glacier Bay fjord, forcing out the Tchukanedi Tlingits and denying entrance to Captain Vancouver. Why the asynchrony? Why, of the national park's 17 current tidewater glaciers, are six advancing, three retreating, and eight holding their own? Photo Station 3 We have rowed ashore on the west side of Johns Hopkins Inlet to photograph the glaciers from a position first used decades ago by Dr. William O. Field, of the American Geographical Society. This station is simply a rounded, glacier-polished outcrop of white rock partly veneered by a mat of dryas runners rooted nearby. A low stone cairn holds a jar with a registry of those who have made official photographs here. It requests anyone who takes unofficial pictures to send copies to the Society to enhance the record. There are only four entries, beginning with 1958. The position is stunning. We see the Johns Hopkins and Gilman Glaciers clearly and half a dozen high peaks, including Mount Crillon, almost 4,000 meters (13,000 feet) high. I talked with Dr. Field a few years ago in New York City. White haired, the epitome of a gentleman-scholar, he is dean of those who have studied Alaskan glaciers. From memory he recited which glaciers were advancing, which retreating, and in what years. As a young geographer he had pondered the small amount of ice left in the United States compared to its dominant role in shaping the land. That's when I got hooked," he told me. In 1926 on his first trip to Glacier Bay he noticed immense changes in the ice positions documented by pioneering glaciologists beginning in the late 1800's. Harry Reid, for example, had written about "changes expected in the next 50 years." Where Reid's map showed solid ice, Field watched whales and seals. The ice was gone. "You need continuity in a record," he told me. "Otherwise there's no way to see what's happening. The Johns Hopkins Glacier, for example, has advanced a mile since I first saw it in 1926 and it's still coming. Small glaciers show change more quickly than vast icefields can. Greater accumulation than normal, or more melting, and they respond almost right away. Yet glaciers aren't simply barometers of climate. There's more to it, especially with tidewater glaciers." The lack of glacier documentation had launched Field's career. Getting data takes remarkable persistence, partly because of the mammoth compilation needed and partly because of isolated and difficult working conditions. "You need triangulation to keep track of what an ice front is doing, but maintaining usable triangulation points gets tough at times," Dr. Field reminisced. "You may go back and find a station worthless because alder has grown so much you can't see out, let alone do any surveying or even take a picture. "Or if the ice is advancing, you have to move the station out of its way. If it's receding, you still have to move so as to stay close enough to do any good. In the 1940's we watched the Grand Pacific Glacier advance from Canada back into the U.S. We'd set up a station and it'd be obliterated before we could get back on another trip. Access was a problem, too, even if the station was still there. We had a real battle getting to the photo point between the Margerie and the Grand Pacific. The beach we needed to land on often was completely blocked by floating icebergs. And the calving of new ones set up shock waves that kept us alert the times we did go ashore." Field said that tidewater glaciers "confuse the whole picture" in measuring past climates. As an oversimplification, assume the steady nourishing of a glacier by yearly snowfall. Once equilibrium is reached, this ice should neither thicken nor thin, advance nor retreat. Given present climate, this fairly well describes most ice tongues in Glacier Bay National Park and Preserve except for those that reach saltwater. These cause the confusion, but research aboard Growler has contributed to understanding them. Receding tidewater glaciers reach into deep water. Advancing or stable tongues end either on marine shoals or where the heads of inlets rise above sea level. If deep water spells retreat, what's the depth where tidal glaciers are advancing? Shallow. Usually less than 80 meters (260 feet). Why? The glaciers themselves make it so. They advance only if they've built a protective shoal at the snout, by dumping rock debris. This forms an underwater terminal moraine and provides a partial barrier between the ice and the erosive action of sea water. By plucking material from the up-slope of this ridge and redepositing it on the down-slope, a glacier can keep advancing along even a very deep waterway. How fast? Perhaps one to three kilometers (0.5 to 2 miles) per century. Eventually the ice may become so extended that the amount lost from the surface melt and calving matches the snowfall feeding the upper glacier. At this stage, balance is so precarious that even a slight retreat causes the snout to back off its shoal and re-enter deep water. Irreversible retreat then continues until the glacier reaches shallow water, usually at the head of tidewater. There it stabilizes, at least until it builds enough shoal to begin anew, slow advance. Sometimes I resent the name Johns Hopkins for this inlet. It comes from an early-day university expedition here. It struck me as audacious to make an institutional trophy of such scenic magnificence. Bob Howe, park superintendent when I first visited here, clamped a moratorium on further naming of peaks, valleys, waterfalls - or anything. He felt there should be places where humans experience the pristine without presuming to label. The gift shop manager of a cruise ship told me she put up a closed sign during her first trip into Johns Hopkins Inlet. "Come to the upper deck if you need film," her note read. "The shop will reopen after we leave Johns Hopkins." It's that beautiful. Reid Inlet We anchored Growler about 0200 this morning. We'd eaten another midnight dinner after finishing the Johns Hopkins depth readings and hiking across the Topeka Glacier outwash, looking for fossil wood. We debated whether to stay in Johns Hopkins or run to Reid Inlet. Austin decided to run because we might be too tired to stand effective watch through the night. There was too little pack ice in Johns Hopkins Inlet to hold Growler safely free of the sidewalls as we drifted. Two other vessels also were running, their distant lights ghostly companions for the late, weary hour. One must have been Explorer, the park concession boat that drifts in the pack ice off the Margerie Glacier through half the night, giving passengers a unique experience of the upper bay. The other probably was a commercial fishing boat. Harry Reid's 1890 map of this inlet now bearing his name shows nothing but ice here. No land at all. Even in the 1940's, when Joe and Muz Ibach built a distinctive little cabin and began mining pockets of gold ore high on the cliffs, the Reid Glacier had drawn back no farther than the toe of their beach. Now you can boat 6 kilometers (4 miles) into the inlet. After breakfast this morning we motored Growler's dory across from our anchorage, following as close as is prudent to the bulging ice face. "The glacier must be advancing," Austin said. "Look at the push moraines." He pointed out low ridges of rock and gravel slightly ahead of where ice is pressing against the inlet's sidewall. Circular mats of dryas are half swallowed by the advance. Sheer crevasses split the ice where its leading edge has thrust across the land. They form 50-meter (164-foot) slits clearly visible against the sky. Aboard Growler I have been seeing advancing or stable glaciers, yet other glaciers in the park are rapidly withdrawing. Muir Glacier has gone back 40 kilometers (25 miles) since 1890 when Reid mapped its terminus barely above the inlet's junction with Glacier Bay. In the years my husband, Louis, and I have been coming to the park we have seen the Muir front separate from the Riggs Glacier and retreat far up the inlet. Austin says it has only a few kilometers to go to reach the head of tidewater. Elevation explains why some glaciers advance here while others withdraw. Tarr, Johns Hopkins, and Reid Inlets all finger from exceedingly high peaks. Plateaus feeding their ice typically stand 2,000 meters (6,500 feet) high and are subject to prodigious snowfall. The park's retreating glaciers, on the other hand, derive from elevations averaging about half that high. The uplands near Glacier Bay's mouth, where ice is gone, rise little more than 350 meters (1,100 feet) overall. This difference in park elevations separates northwestern advancing ice from eastern receding ice. And the Brady Icefield's immensity seems to influence its own weather. The icefield chills moisture-laden clouds from the Pacific and triggers their glacier-nourishing release. Surprisingly small temperature differences account for radically varying glacial effects. The Wisconsinan Ice Age was only 5 to 6 degrees Celsius cooler than today. The following warm period averaged perhaps one degree warmer than today. During the Little Ice Age here, the elevation above which more snow fell in winter than melted in summer was about 830 meters (2,700 feet). Dr. Field places this point today at 1,600 meters (5,200 feet) - except for the Brady Icefield where it's half that. No wonder the only glaciers here likely to advance now are those with their heads high in the mountains. The dice are hopelessly loaded against the others, aside from the peculiarities of tidewater ice. Viewed on a time scale of millennia, all glaciers are responding to climate. They are asynchronous only in terms of centuries and decades, time scales more comprehensible because they better match our lifespan. What we view as significant events may be minute fluctuations on the millennial scale, which is, for glaciers, the more true scale.