$Unique_ID{bob00998} $Pretitle{} $Title{Glacier Bay Tidewater Glaciers} $Subtitle{} $Author{Kirk, Ruth} $Affiliation{National Park Service;U.S. Department Of The Interior} $Subject{ice glacier muir bay feet meters glaciers pacific time water see pictures see figures } $Date{1983} $Log{See Muir Glacier*0099801.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 Tidewater Glaciers In a small way, I once touched time. It was July and my husband, Louis, and I were camped in Reid Inlet, an exquisite fjord fingering off Glacier Bay's main, upper waterway. Our tent was pitched near a 1940's gold miner's shack, which that summer was serving as headquarters for park ranger Ole Wik and his wife, Manya. Rock peaks and ridges walled our horizon. At the inlet's head a glacier tongue calved icebergs directly into saltwater. From basketball to Detroit limousine size, these ice chunks rode the currents and stranded ashore on each outgoing tide, making the beach a sculpture garden. Manya lugged small stranded bergs home in pails hung from a shoulder yoke. The ice turned a pit dug in the coarse upper beach gravel into an icebox. One evening, the Wiks and Louis and I decided to make ice cream in an old hand-crank freezer. Out from the pit came fresh eggs, which Manya mixed with powdered milk dissolved in creek water and sweetened with honey. Ole and Louis chipped salvaged bergs and packed the ice fragments into the freezer. We turned the crank till it would turn no more and then spooned out the ice cream. Icebergs floated on the tide just offshore. We sat reveling in the 11 p.m. sunset and feasting on the ice cream. A cormorant, its sleek body and upright neck a dark silhouette against the water's pink tint, rode one berg. New bergs sporadically broke from the glacier, their birthing thunder a syncopation for the evening's hush. Ole mused aloud on our having used the iceberg's fossilized cold to freeze the ice cream. For the ice it concluded unknown decades of an existence begun as fluffy snow and then compressed to ice, owing to the sheer weight of snow accumulating above it. By the Grand Pacific Glacier Reid Inlet ice cream comes to mind now, four Julys later, as I cook breakfast aboard R.V. Growler, a U.S. Geological Survey ice research boat. Oatmeal bubbles on the galley's oil range as I set out the corn muffins I've baked. The big galley table is at once workbench, library desk and center for food preparation, eating, and socializing. Five of us are aboard. In charge is glaciologist Austin Post - tall, strong, with a grizzled beard that hangs to his chest and gentle eyes that laugh. His assistants, college-age, capable, enthusiastic, are David Janka, Emily Chase, and Austin's son Charles Post. My role is as observer and photographer. For two hours we've been taking depth readings in front of Tarr Inlet's Grand Pacific Glacier. Its ice, along with that of the Margerie Glacier, blocks the extreme upper end of Glacier Bay. Data recorded by Growler's electronic sounder will make it possible to chart the bottom contours here. The contours will help in understanding tidewater ice, which responds to various factors aside from climate. Why, for example, is the Grand Pacific Glacier advancing, while just to the east, the Muir Glacier has been rapidly retreating for a century? What accounts for such diverse behavior in the same area? Glacier ice today whitens a tenth of the world's land surface, as much as is now farmed. A few thousand years ago glaciers covered triple this area, as they someday surely will again. Boston's Bunker Hill is a drumlin left behind by glacier ice. Erratic boulders dot Manhattan's Central Park, transported from Canada by glacier ice. Duck hunters in Minnesota set decoys on pothole lakes formed by melting ice remnants. Plains farmers grow wheat in loess, windblown glacial sediment. French vineyards are also in loess. Drink French wine and you toast the Ice Age. Yet despite the magnitude and recurrence of glaciers, knowledge of them is little more than well begun. Glacier Bay is one of the widely recognized field laboratories for glaciology. Growler is in Glacier Bay as part of a continuing study of tidewater ice. Austin Post can visualize these ice tongues and how they behave. For 20 years he has been making aerial photographs of glaciers from the Andes to the Aleutians and painstakingly mapping their changes. Austin does not merely rejoice to know that the world is not only blue and green but also white. He prefers the white. When I came aboard Growler, he asked me about the weather in Seattle. "Sunny and hot," I said. "That's awfully hard on the ice," Austin muttered in reply. At the wheel Austin is now maneuvering Growler through floating icebergs. They aren't packed solid this morning and we can work to within one-third kilometer (1,000 feet) of the Grand Pacific's ice face. We won't go closer because of danger from falling ice, but we'll send a small, radio-controlled skiff to bump against the glacier snout and read the water depth there. The glacier front is not floating. It rests on a rubble ridge of its own making. Emily, Dave, and Chuck are with Austin in the wheelhouse, correlating Growler's precise position with the depth-sounder record and with Polaroid pictures of the radar scope. I can be spared to cook, but everyone else is needed for the readings. It's 0800 now. We've been underway since 0630 and will soon cut the engine to drift with the pack ice and eat breakfast. A moment ago we were swept off course by a melt torrent draining from under the glacier. No depth reading registered until we worked free of its flow, because the stream disgorges so much suspended mineral material that the signal from our depth sounder dispersed instead of striking bottom and bouncing back. Even the water surface is gray with glacial flour, bedrock ground to powder by the pressure of moving ice. Away from the ice front the gray becomes turquoise as the silt mutes but no longer dominates the clear, deep blue of open water. Often distinct color bands persist, their moire pattern maintained by the water's different temperatures and salinities. Such banding may reach all the way to Icy Strait, 70 kilometers (43 miles) from the nearest tidewater glaciers. We terrestrials think of seawater as homogeneous. It's not. Nor is a glacier just a mass of frozen water. It is ice, plus flowing water, plus a vast amount of rock debris scoured, rasped, and plucked from the mountains where glaciers are born and from the valley walls and bottoms they inch across en route downslope. In the color banding of a fjord's water surface you witness the sedimentation process that in time fills in enormous submarine troughs and turns waterways into valleys with freshwater streams and wildflowers. Out Growler's porthole the far side of the Margerie Glacier is so blackened with rubble that it looks like rock. Only a melt sheen identifies it from this distance as glacier ice. Directly ahead of us, moraines of rock debris streak the length of the Grand Pacific Glacier like ribbons. At the sides of the ice face they show as tilted layers dipping into the water. Moraines form as rock tumbles and slides from steepened slopes onto the glacier surface, there to ride the ice and eventually break free as part of an iceberg, or to be released by melt. Moraines are among the legacies of glaciation. They form abrupt ridges of loose rock, gravel, and sand often several-score meters high and extending for long distances. Though in time moraines may become upholstered with plants, their origin remains easily recognizable. When mineral debris is dropped directly beneath a glacier it may form hills and short ridges known as kames and drumlins, or, if deposited by a subglacial stream, as eskers. Last evening we anchored Growler a half-hour's run south of the Margerie ice front, then hiked up a side drainage and sat at dusk watching a loon paddle across a small lake impounded by an esker. Slices of time seemed separated from eternity's flow and laid before us. We had walked through a carpet of dryas plants shaggy with seedheads. Dryas can pioneer poor soil and so can quickly form a green aftermath of glacier ice. We had hoped to find glacio-marine - clay lumps dropped, usually, from floating icebergs - remnants from millennia ago when seawater covered where we sat watching the loon. Floating bergs, the white peaks, and the processes of mineral transport and deposit, have all repeatedly characterized the Glacier Bay scene. Until recently, geologists believed that the last million years had brought four major ice ages. Now they see these as composite glacier advances, retreats, and re-advances. The number of such pulses was closer to 40 than to four, with one series often hard to discern from another. Expanding glaciers clear virtually everything movable from their paths, so nothing more than traces of early glaciations are likely to remain. One such trace lies along the outer coast of Glacier Bay National Park. Marine tillite, glacial debris deposited in seawater, is there interbedded with layers of siltstone and sandstone for a total thickness of nearly 2,000 meters (6,500 feet). The ancient tillite formed by the same mineral dumping process I've been watching this morning. It comes complete with the rafted lumps such as we sought without success last evening - the sort that ride the icebergs I see out the porthole now. Shells date the layered outer-coast sediments to about 15 million B.P. (before present). A park research biologist once told me he found a fossil beech leaf in the deposits. It must have been blown or washed seaward to settle in the ocean bottom ooze. To have endured for 15 million years seems extraordinary; to be a beech leaf even more so. For that testifies to a scene far different than today's. Glacier ice was then juxtaposed with deciduous forest. Nowhere does such a situation exist today except in Chile where a relative of beech thrives close to ice. For most of southeast Alaska, the signs of early glaciation are not deposition but erosion. Sharply sculpted high peaks are those plucked by ice. Lower rounded contours were overridden. You can see this craggy horn peaks to rounded and polished bedrock and so pinpoint the level of a former glacier. In lower Glacier Bay this line comes at about 1,300 meters (4,200 feet). The period from about 30,000 to 10,000 B.P. brought the most recent worldwide glaciation, known in America as the Wisconsinan because the southern edge or terminus of a vast ice sheet sculpted much of that state's current topography. The Glacier Bay elevation region - and practically all high latitudes and elevations - surrendered to ice during this time. Juneau lay beneath a white shroud 1,500 meters (5,000 feet) thick. At Cape Spencer on the park's outer coast the ice was still at least 900 meters (3,000 feet) thick, with its leading edge somewhere far beyond today's coastline. Oddly, however, parts of the shore were not veneered by this ice. It may be they escaped because a geologic fault at the western base of the Fairweather mountains acted as a gutter and shunted off encroaching ice. Such faults are cracks in the Earth's surface. This one marks where the crustal plate comprising the Pacific Ocean floor, abuts the crustal plate bearing the North American continent. California's famous San Andreas Fault is somewhat comparable. The Fairweather rift splits off land from Icy Point to Russell Fjord, north of Yakutat. Bedrock is out of alignment along opposite sides of the fault. In fact, whole provinces have slid northward as the oceanic plate collides with the continental plate and heaves up the mountains. Certain rock found at sea level south of Icy Point stands north of the Point at an elevation of more than 3,000 meters (10,000 feet). Less active faults underlie both Glacier Bay and Lynn Canal. Above Tarr Inlet It is afternoon and Dave and Emily and I have climbed onto the highest terrace of the slope above the Grand Pacific snout. Dave's altimeter shows our elevation as 269 meters (882 feet). A multi-decked cruise ship drifting among icebergs near the glacier face looks from here like an inconsequential dot. People on deck to watch bergs calve off must see the glacier front as immense. At 60 to 80 meters (200 to 260 feet) high and 6 kilometers (3.75 miles) across, it is. From our vantage point you see how much more glacier there really is than shows from the water. Grand Pacific flows as an infinity of ice coming from far back in the mountains. Except for crevasses near the Snout, its surface looks like a broad white highway, which is how several coastal Alaskan glaciers served Indians and prospectors traveling to and from the interior. Using Grand Pacific as a conduit, wolves and bears have extended their range onto Glacier Bay lands recently melted free of ice and beginning to host life again. From where we sit it's easy to imagine Tarr Inlet stripped of today's ice, seeing instead either a continuation of today's waterway or a broad terrestrial valley bottom. As recently as the 1920's the Grand Pacific melted its way out of the United States and 2 kilometers (1.2 miles) into Canada. That gave Canada a potential site for her northwesternmost seaport. But by 1948 ice again moved forward as far as the border. The Glacier Bay bedrock trough is tremendously deep, dropping to 550 meters (1,800 feet) near Gilbert Island. Muir Inlet reaches about 375 meters (1,200 feet), a considerable depth, yet the inlet completely filled with gravel following withdrawal of the Wisconsinan ice! This fill stood higher than present sea level, developing soil and a spruce-and-hemlock forest. Side valleys, dammed by the gravel, seem to have held lakes, because traces of glacial outwash gravels cling 250 meters (820 feet) above today's saltwater shores, and lakebed sediments are still in place. Dr. Richard Goldthwait, emeritus professor at Ohio State University, believes that the fill in Muir, Wachusett, and Adams Inlets probably averaged 150 meters (500 feet) deep and 5 kilometers (3 miles) wide for a cumulative 80 kilometers (50 miles) of length. Except for mere whispers, this stupendous volume of gravel fill is now gone. Readvancing ice swept it into the Beartrack Cove area and on southward. The broad Gustavus flatlands are partly old Muir gravel fill. Wisconsinan glaciers melted back perhaps 11,000 years ago and probably stayed back until about 3,500 years ago, when harsh climatic conditions again favored glacier expansion. Worldwide this Little Ice Age was not dramatic. At Glacier Bay, however, snowfall produced ice more than 1,000 meters (3,200 feet) thick and pushed the glaciers far forward. A tongue of ice once more filled the entire Glacier Bay fjord and bulged out into Icy Strait. This dammed Muir Valley and backed up an enormous lake there that drowned the forest. About a thousand years after the glaciers' encroachment into the main Glacier Bay fjord, an ice tongue began to advance down Muir Valley. At the outlet it was blocked by the glacier already there. Unable to thrust farther forward, this new ice ponded and flowed back on itself, filling depressions along lower Muir Inlet to such depths that remnants still haven't melted today. They are popular destinations for hikers and give geologists a look at how melting glacier ice has produced much of today's northern latitudes topography. The ebullient, voluble, knowledgeable, and renowned John Muir was an early exponent of the continental glaciation theory in North America. He canoed north from Fort Wrangell in October 1879, coaxing his Tlingit Indian paddlers onward against their judgment. Fall struck them as a foolish season for venturing among icebergs. But for Muir ice was the reason for the journey. Aged 41, acclaimed champion of all nature, specifically fascinated by glaciation, Muir became the first Glacier Bay sightseer to write extensively and glowingly about the wonders of what now is the national park. His first trip was brief, but in the summer of 1880 and again in 1890, Muir returned. By the time of his third trip, tourists were visiting Glacier Bay aboard sidewheel excursion steamers. Eliza Ruhamah Scidmore wrote in a National Geographic article of "stopping, backing, and going at half speed to avoid the floating ice all around [which] occasionally was ground and crunched up by the paddle wheels with a most uncomfortable sound." The Muir Glacier - newly named for the famed naturalist - had scarcely begun its retreat at that time, though the ice filling Glacier Bay proper had drawn back 60 kilometers (37 miles) in the century since British Captain George Vancouver had noted its presence in 1794. This glacial unzipping is the fastest known anywhere, anytime. [See Muir Glacier: Mad wreckage of the retreating Muir Glacier ice front chokes adjacent waters. The glacier retreated about 5 kilometers between 1972 and 1982. It has retreated more than 25 kilometers (15 miles) in this century, at widely varying rates.] Fortunately for the understanding of Glacier Bay's chronology, Harry Fielding Reid, a pioneering glaciologist, arrived here in 1890, about 30 years after the Glacier Bay unzipping had exposed the Muir Glacier for the first time. Through the summer of 1890 and again two summers later, Reid explored by rowboat and on foot, lugging a cumbersome theodolite and plane table for mapping glacier positions. "We once approached to within a quarter mile of the ice cliffs of Muir Glacier, which towered impressively above us," Reid wrote. "Suddenly a large berg broke off, followed immediately by a second, and then several arose from below. Great breakers which must have been 30 feet high, rushed forward, but fortunately subsided into an even swell before reaching us. The fragments of ice spread out with great rapidity and in a few minutes quite surrounded our boat." The Grand Pacific Glacier was then fused with the Margerie, their joint terminus barely separated from the Johns Hopkins Glacier. Reid wrote that the continual calving of that great ice cliff, nearly 10 kilometers (6 miles) long, was "keeping the inlet well covered with floating ice and the air pulsating with the thunder of its fall." No wonder the Tlingits thought John Muir reckless, though he gloried in the calving bergs' "awful roaring, tons of water streaming like hair down the sides, while they heave and plunge again and again before they settle in poise and sail away as blue-crystal islands, free at last . . . ." John Muir, too, had touched time.