Alaska stud­ies glacier’s surges

China Daily (Hong Kong) - - SCIENCE & TECHNOLOGY - By KIRK JOHN­SON

JUNEAU, Alaska — The idea that glaciers change at a glacial speed is in­creas­ingly false. They are melt­ing and re­treat­ing rapidly all over the world. But the un­pre­dictable flood surges at the Men­den­hall Glacier, about 20 kilo­me­ters from down­town Juneau, Alaska’s cap­i­tal, are es­pe­cially wor­ri­some as global tem­per­a­tures and cli­mate vari­abil­ity in­crease.

Start­ing in July 2011, and each year since, sud­den tor­rents of wa­ter shoot­ing out from be­neath the glacier have be­come a new facet of Juneau’s brief, shim­mer­ing high sum­mer sea­son. In that first, and so far big­gest, mea­sured flood burst, an es­ti­mated 37 bil­lion liters gushed out in three days, threat­en­ing homes and prop­erty along the Men­den­hall River that winds through part of the city. There have been at least two smaller bursts this year.

“That first one caught us by sur­prise,” said Tom Mat­tice, the emer­gency pro­grams man­ager and avalanche fore­caster for Juneau.

That the Men­den­hall Glacier is thin­ning, and has been for decades, is only part of the ex­pla­na­tion. Wa­ter from snowmelt, rain and thaw­ing is are also com­bin­ing in new ways, re­searchers said — first pool­ing in an ice­cov­ered de­pres­sion near the glacier called Sui­cide Basin, then find­ing a way to flow down­hill.

What prompts a surge — and the ur­gent search for a way to an­tic­i­pate and pre­pare by sci­en­tists and safety of­fi­cials like Mr. Mat­tice — is pres­sure. As wa­ter builds up in the basin and seeks an out­let, it can lift por­tions of the glacier ever so slightly, and in that lift, the wa­ter finds a re­lease. Un­der the vast pres­sure of the ice bear­ing down upon it, the wa­ter ex­plodes out into the depths of Men­den­hall Lake and from there into the river.

Glaciol­o­gists even have a name for the process, which is hap­pen­ing in many places all over the world as cli­mates change: jokulh­laup, an Ice­landic word usu­ally trans­lated as “glacier leap.”

“We don’t have a sense yet how much of a threat this poses, or how much wa­ter you could store up there,” said Ja­son Amund­son, an as­sis­tant pro­fes­sor of geo­physics at the Univer­sity of Alaska South­east, in Juneau.

What el­e­vates the con­cern is the prox­im­ity of peo­ple. Glaciers may be leap­ing in many places, but it hap­pens mostly in iso­la­tion. The roughly 20-kilo­me­ter-long Men­den­hall, by con­trast, is one of the most vis­ited glaciers in the world, and an ur­ban one. About 400,000 tourists a year, 80 per­cent of them from the cruise ships that stop at the Port of Juneau, are drawn to the glacier.

“We’re a drive-up glacier,” said Nikki Hinds of the Men­den­hall Glacier Vis­i­tor Cen­ter, which is op­er­ated by the United States For­est Ser­vice. “In how many places can you have that?”

This sum­mer, glacier-mon­i­tor­ing in­ten­si­fied. A pres­sure trans­ducer to gauge wa­ter buildup was in­stalled in a deep crack on the edge of the basin, with a satel­lite link send­ing back real-time data about the glacier’s hid­den wa­ter­works. A time-lapse cam­era was also po­si­tioned at the main pool­ing site for the first time to track bulges in the ice that could sug­gest dammed-up wa­ter.

Like glaciers the world over, the Men­den­hall has thinned and re­treated more than a hun­dred me­ters since vis­i­tors first started com­ing here in the late 1800s. Long-term cli­mate mod­els sug­gest a warmer, wet­ter pat­tern in this part of Alaska, which could have its own strange rip­ple of con­se­quences for the Men­den­hall and the peo­ple who love it, study it and live by it.

Jamie Pierce, a moun­taineer and re­searcher at the univer­sity, was out on the Men­den­hall ice on a re­cent af­ter­noon, check­ing the in­stru­ments. Af­ter rap­pelling about 15 me­ters to the trans­ducer, he found it com­pletely dry, sug­gest­ing that the wa­ter was find­ing an­other chan­nel or an­other damming point, other than the one sus­pected of caus­ing the trou­ble.

Mr. Pierce said, “The big­gest thing we don’t know is what’s block­ing what.”

‘‘Glacier leap,’’ or melt­ing that leads to a sud­den re­lease of wa­ter, is oc­cur­ring at Men­den­hall Glacier in Juneau. Jamie Pierce, a re­searcher in Alaska.

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