We’re entering the best time of year for fans of glaciers.  The high-country rivers of ice are getting their annual nourishment from winter’s snows–probably not enough, as Yosemite National Park geologist Greg Stock tells us: “Glaciers are getting about the same amount of snowfall each winter but they’re seeing a lot more melt in summertime because of those warmer temperatures.”

A database called Glaciers of the American West posits that, “Perhaps glaciers are the clearest expression of climate change.”  But within that National Science Foundation-funded database can be found a few growing glaciers–curious exceptions that buck the general melting trend.  Cherry-picking those exceptions allows some global warming skeptics to suggest we should be preparing for the next ice age (see here and here for examples of this). However, a closer examination of the anomalous glaciers suggests that unique circumstances are more likely at work.

Crater Glacier on Mount St. Helens in southwest Washington State is a dramatic example of a growing glacier.  The glacier formed in the shaded recesses of the high elevation crater left by the catastrophic 1980 eruption of the volcano.  USGS research hydrologist Joe Walder told us the mass of ice and rock is advancing some 300 feet per year.  This time lapse video (file will download) provided by the U.S. Geological Survey shows why glaciers are also known as “rivers of ice.”

Another view from above shows how Crater Glacier got squeezed and pushed around when Mount St. Helens reawakened in 2006 and extruded a new lava dome.  That the young glacier survived the renewed eruption is remarkable by itself.  The fact that the horseshoe-shaped glacier is gaining mass indicates just what a perfect setting Mother Nature created at the volcano.  The north-facing crater acts like a catcher’s mitt reaching toward the moist jet stream.

Mount Rainier, also in Washington State, is the most heavily glaciated peak in the Lower 48 states.  On Rainier’s east flank, Emmons Glacier is advancing. The National Park Service offers this myth-busting explanation:

“The Emmons Glacier experienced a rock avalanche in 1963, which covered part of the glacier with a layer of rock debris. This debris now insulates the ablation (melting) zone of the glacier from sunlight and warm air temperatures and the melting of the glacier is smaller than from an otherwise clean glacier. Because melting is reduced, but the ice flow is the same, the glacier is advancing. This response has nothing to do with climate change.”

Something yet again different appears to be happening at northern California’s Mount Shasta. A research team from UC Santa Cruz documented 50 years of nearly continuous expansion of the two largest glaciers on Mount Shasta.  The researchers theorize in the journal Climate Dynamics that Shasta’s glaciers are benefiting from a warming Pacific Ocean. A warmer ocean means more evaporation, and hence more moisture blows over the high peaks near the coast.  Because of Shasta’s height, the enhanced precipitation mostly falls as snow, adding to the mass of the glaciers.

Portland State University glaciologist Andrew Fountain says no one has yet explained to his satisfaction why glaciers on peaks immediately to the north and south of Mount Shasta are not likewise growing.  It is as if a “snow gun” is aimed directly at Shasta’s 14,162-foot summit.  But he doesn’t lose sleep over that issue because Fountain and the other glaciologists who have studied Shasta do not expect the glacial advance to last.  Their climate models call for the snow level (elevation) to rise.

“We do expect it to be a temporary phenomenon,” Fountain said.  “The modeling done down on Mount Shasta expects the glaciers to retreat within the next decade or so, if they’re not already.”

Tom Banse’s radio feature on the West’s growing glaciers airs Monday morning on The California Report.