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yes

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Alaska's Glacier Bay has fascinated

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naturalists and glaciologists for

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centuries named the National Monument in

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1925 and a national park in 1980 Glacier

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Bay today attracts more than 250,000

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visitors a year just 200 years ago the

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entire Bay was covered by glacier ice

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with the help of ground and satellite

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measurements study of the recession of

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the glaciers of Glacier Bay as well as

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in other areas is providing us with

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important clues about changes in global

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a glacier is a dynamic system consisting

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of snow ice and often rock debris that

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transports material from higher

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elevations where snow accumulates to

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lower elevations where snow and ice melt

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snow becomes glacier ice over time when

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the pressure of increasing layers are

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snow accumulating year after year

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transforms the snow first into fern

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which is very dense snow and eventually

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into ice today there are over 200

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separate smaller glaciers in Glacier Bay

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National Park to the delight of park

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visitors who view them from cruise ships

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private boats and kayaks glaciers at the

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head of tar inlet of the most

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spectacular these include the Grand

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Pacific and the margaery together they

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comprise three kilometers of ice front

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which is cowling into the sea the Johns

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Hopkins and Marjorie glaciers are each

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about one-and-a-half kilometres wide and

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22 kilometers long they are both dwarfed

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by the Grand Pacific glacier a tall

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towers 60 to 90 meters above the water

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at their term and I with another 120

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meters below the water surface these

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glaciers calve icebergs into the ocean

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on a regular basis grilling visitors

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written records of the glaciers in

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Glacier Bay began with George

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Vancouver's visit in 1794 ground

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observations beginning in the late 1800s

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and ground-based and satellite

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measurements in recent years have shown

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that many glaciers in and near Glacier

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when a glacier recedes water from the

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melting ice is released into the ocean

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and sea level rises though the greatest

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potential for sea level rise is from

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melting of the Antarctic and Greenland

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ice sheets the small glaciers of the

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world such as those in Glacier Bay would

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contribute to a sea-level rise of about

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six-tenths of a meter if they were to

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melt completely precise measurements of

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glacier changes may be made by

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ground-based surveying the light

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glaciologist William O field began

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photographing and measuring glaciers in

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Glacier Bay in 1926 many of the glacier

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terminus positions map by field and his

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colleagues are shown on the map of

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Glacier Bay prepared by the National

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Park Service glacier work in the early

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part of this century was even more

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difficult and hazardous than it is today

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scientists had to roll through iceberg

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laden water to reach many of the glacier

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fronts detailed measurements in Glacier

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Bay made by field and others have

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provided an excellent description of the

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dates and magnitude of changes in the

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the once enormous Muir glacier located

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in what is now mere Inlet in the East

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arm of Glacier Bay was named for John

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Muir the famous naturalist and explorer

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who visited Glacier Bay in the late 19th

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century in 1905 just 26 years after

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mirrors first visit Fremont Morris wrote

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formally the mirror presented a

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perpendicular front at least 200 feet in

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height from which huge Berg's were

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detached at frequent intervals the sight

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and sound of one of these vast masses

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falling from the cliff or suddenly

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appearing from the submarine I slit was

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something which once witness was not to

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be forgotten it was grand and impressive

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beyond description fortunately the

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recent changes in the mirror have not

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increased its impressiveness from a

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scenic standpoint instead of the

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imposing cliff of ice the front is

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sloping and seems to be far less active

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than formerly the Muir glacier is now

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but a small remnant of its former glory

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and has nearly retreated up out of the

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ocean in fact many of the large

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Tidewater glaciers that John Muir first

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observed in 1879 have been reduced to

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small glaciers that terminate on land

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land that is uncovered as glaciers

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recede from its plant and animal life to

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appear and flourish beginning with the

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launch of the first Landsat satellite in

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1972 we have with a spatial resolution

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of up to 30 meters been able to acquire

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detailed satellite images of the

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glaciers of Glacier Bay and measure

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changes in those glaciers to satellite

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sensors the multispectral scanner and

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the more advanced thematic mapper allow

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us to measure glaciers without having to

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maps drawn by earlier explorers of

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Glacier Bay can be registered to or

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overlaying on satellite images using

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computer techniques common stable points

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between the map and the images are

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located and digitally overlaying using

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image processing techniques one image is

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stretched in relationship to the other

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once the images are registered we can

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measure changes in glacier terminus

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positions from the time of the earliest

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using computer techniques we can

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register elevation data to satellite

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images this allows us to obtain a

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three-dimensional perspective and

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actually appear to fly by an area

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measurements of the Muir glacier have

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shown that the terminus retreated up the

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mirror inlet at a rate of about four

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tenths of a kilometer per year between

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1794 and 1892 for a total retreat to

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more than 40 kilometers satellite

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measurements derived from images

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acquired in 1973 1980 1983 and 1986 show

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that the Muir glacier terminus went back

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more than seven kilometres between 1973

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and 1986 with most of that retreat

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mcBride glaciers the most active glacier

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and mirror inlet it is still receding

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and over the last two decades has formed

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an impressive Inlet as recorded by

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satellite datum the terminus of the

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McBride glacier retreated almost three

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kilometres between 1973 in 1986 and the

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nearby Burroughs glacier shrank

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considerably filling lakes with its

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meltwater note the increase in the

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amount of vegetation the vicinity of

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burrows glacier in 1986 the burrows is

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now a dying ice field having been cut

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still other glaciers have been in

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equilibrium or advancing some like the

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Johns Hopkins have stopped their retreat

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and have advanced during the period

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covered by the satellite record also the

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lamp Lou Reed Marjorie and Grand Pacific

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glaciers are all advancing at this time

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the nearby Brady glacier has been

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advancing since 1794 however the major

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feature of Glacier Bay is the

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large-scale retreat of its Tidewater

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glaciers and both mirror and tar inlets

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Tidewater glaciers like the mirror and

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the Marjorie terminate in the sea

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Tidewater glaciers follow their own

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cycles that are independent of

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short-term climate changes there are

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also non Tidewater glaciers near Glacier

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Bay many of which are receding recession

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of non Tidewater glaciers in the area is

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probably due to amelioration of the

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regional climate meteorological data

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from the nearby stations at juneau Sitka

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and Yakutat show a tendency toward an

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increase in average summer air

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temperature since about nineteen forty

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combining the extensive records of

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explorers beginning the late 18th

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century with more recent efforts of

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glaciologists and computer scientists a

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wealth of information has been obtained

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about the d glaciation of Glacier Bay

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Alaska as these glaciers and others

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continue to change or if they remain

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stable over time the satellite record

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will permit assessment of the impact of

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changing climate on the glaciers and

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many of the non Tidewater glaciers are

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excellent indicators of regional climate