Module IX - Ice Sages

ENGAGE

Glaciologists--Ice Sages
Imagine a mountain valley catching the moisture that falls within its boundaries and funnels it down into a lake sprawling across a low lying area. When the precipitation exceeds the capacity of the lake, it spills over into a river that flows down toward sea-level. Sounds reasonable and familiar. We've all seen it.

But what if the moisture that falls in the high mountain valley is snow that doesn't melt each spring? What's different? Erosion and sedimentation processes notwithstanding, any glaciologist will tell you, not too much is different -- if you've got the time to watch.

Snow falling at high elevations probably evaporated from the surface of the tropical ocean no more than a couple of weeks prior. This accumulating young snow compresses under its own increasing weight over time turning into dense, clear ice.

When the lake of ice (ice field) fills to overflowing, the plastic river of ice flows out of the confines of its upper reaches and meanders slowly and massively downhill, grinding its own deep valley along the way on its journey to the sea. Same-same.

Inland glaciers flowing out of high mountain valleys until they reach lower, warmer elevations liberate their solid water as liquid rivers off to find the sea. Alaska's coastal mountain ranges host many glaciers that surrender their centuries old cache of water directly into the ocean as ice--tidewater glaciers.

Whether indirectly by river or directly by glacier, water is constantly rejoining the ocean for the first time in many, many years. And it's doing so at a rate that presently exceeds the rate at which it is returned to the mountains as snow.

And like a river, a glacier's rate of flow is determined largely by the amount of precipitation accumulation that fills its reservoirs . Advancing glaciers are driven by accumulation rates that exceed its melting, or ablation, rate.

The Great Recession
Unlike liquid rivers, glaciers frequently change phase abruptly as they descend to warmer elevations. Glaciers that melt faster than they advance are called receding glaciers. This dance between accumulation and ablation, advance and retreat, is expressed over time as a glacier's mass balance.

Most glaciers have been receding since the LGM. But ice sages studying the mass balance of glaciers world-wide have noted recent acceleration in the ablation rates of glaciers, indicating overall increased rate of reduction in glacier mass balance.

Lyrical Lexicon
Left behind the receding ice are the curious landforms unique to the forces of glaciers: esker, drumlin, kettle, moraine, cirque, tarn, kames, varve and arete are just part of the lyrical lexicon of glaciologists describing specific processes and formations that result from the advance and retreat of glaciers. You might be surprised by how many of these post glacial landscape features are part of our common geography.

From the Great Lakes to Cape Cod. From Long Island to Lituya Bay, each is a geologically recent product of the work of glaciers. And each was settled for the first time by the earliest north Americans shortly after the ice melted.

EXPLORE

Teachers' Domain
Earth System-Ice and Global Warming







Documenting Glacial Change






Fastest Glacier







EXPLORE SOME MORE....

Don't Go With the Slo Flo
Glaciers are often compared to rivers in terms of their motion, but to most of us they look solid and static. But what if you could speed-up time?

That's just what the scientists at the Extreme Ice Survey did by placing remote cameras focused on glacial landscapes and leaving them for more than a year. What emerges in the compressed sequence of images is the fluid motion of ice.

Visit the Extreme Ice Survey website and watch a time lapse Vimeo of the Mendenhall Glacier during the 16 months between May 2007 and September 2008.




Helpful Hint: Find out if any Alaska Glaciers are advancing. Visit the USGS - Alaska Glacier Repeat Photography Project. It's an engaging collection of recent and old photographs contrasting many of Alaska's Glaciers over time.


EXPLAIN

• What different kinds of ice loss are evident?
• What factors affect a glaciers mass balance?
• How does glacial melt affect sea level?
  

EXTEND

• Use Google Earth to explore and photograph examples of post glacial features.
  

EVALUATE

• How well do these resources help students understand glacial processes?