Glaciers have a story to tell. The accumulation and ablation a glacier experiences describe the mass balance, or the yearly growth or shrinkage, of the glacier. Glaciologists spend weeks tromping around the ice each summer and examining aerial photographs to keep track of the final yearly firn line and the equilibrium line altitude. By recording the yearly mass balance of a glacier, scientists can actually trace changes in climate. If a glacier has a positive mass balance it is growing and the weather is cold and wet. The balance is negative when the climate is dry and warm. Thus the health of a glacier is highly sensitive to local and global changes in climate.

Keeping track of glacial movement was not always so sophisticated. In the early 1900’s, park rangers used red paint to mark the location of Blue Glacier’s terminus on a rock wall. Until covered by the advancing ice, this crude measurement technique did record variations in the glacier, but scientists now know that advance or retreat does not necessarily reflect the mass balance of a glacier. Movement of the terminus usually accompanies prolonged changes in mass balance, but a short succession of dry years, for example, may not cause the glacier terminus to recede.

The last 50 years of the mass balance story for Blue Glacier is remarkably boring when compared to earlier times. The glacier reached its farthest and lowest position known around 1650. A second maximum occurred 165 years later in 1815. Both early explorers in the area and local Hoh legend recount hearing large explosions coming from a second, and now extinct, icefall. Though now only a rock cliff below the snout, the glacier cascaded down a nearly vertical 500-meter high icefall before reaching a terminus. Between 1815 and 1960, the glacier retreated an estimated 1650 meters up this slope and then remained near this point for about 40 years. Since 1976, however, the mass balance has become increasingly negative and the glacier is now considered to be out of equilibrium with the warming climate.

Tracking the recession of a glacier is more significant when human-induced global warming is causing the retreat. National Weather Service data indicate that average winter temperatures in the Olympic Mountains have increased by 3.3 degrees C since 1948—a rate about five times higher than the global average. Paint is unnecessary when you can almost watch a glacier disappear.


intro | terminology | accumulation | firn | blue | ablation | water | equilibrium | massbalance | movement | crevasse | structure | algae | moraine | debris | erosion
pdf version | glacier glossary | bibliography | about blue ice

Benjamin Drummond 2002