Mt. Kilimanjaro ice fields, glaciers still shrinking, says Hardy

Ice fields on Africa’s Mount Kilimanjaro are rapidly shrinking and thinning, according to a research team including geoscientist Douglas Hardy and colleagues at Ohio State University. They reported in an online early edition of Proceedings of the National Academy of Sciences that “new aerial photo analysis shows that 26 percent of the area covered by ice in 2000 is now ice-free and whereas 79 percent of the area covered with ice in 1912 was ice-free in 2000, 85 percent now is.”

Hardy returned recently from a trip supported by the National Science Foundation to the mountain in northern Tanzania, where he and colleagues took advantage of a very dry period to examine the glaciers and update the ice area loss. Pointing out that glaciers have existed on Kilimanjaro for 11,700 years according to their earlier publication, Hardy and colleagues now predict that they will disappear within decades.

With this paper, the group documents that the glaciers are thinning as well as retreating laterally. Hardy adds, “thinning is now happening quite rapidly, but we can’t be certain how the current rate compares with that at different times in the past. Without any earlier measurements, we must be very careful with such statements.”

“This is the first time any ice thickness or volume loss measurements from Kilimanjaro have been published,” Hardy says.

Another achievement of Hardy’s recent fieldwork was collecting almost 53 pounds of ice samples in only the second attempt to date Kilimanjaro’s glaciers. “For nearly 10 years, we’ve had only one ice-core record of paleoenvironmental conditions in Africa, which our group recovered, in 2000. So reevaluating the chronology before the ice disappears is essential,” he says.

Kilimanjaro is made up of three extinct volcanoes, the tallest of which is Kibo at 19,340 feet (5,895 meters). Hardy and colleagues focused their studies on Kibo’s Northern Ice Field and the Furtw?ngler Glacier, where in addition to the aerial photos they used ice cores, GPS data, historical maps available since 1912, and a network of stakes to measure ice thickness and satellite images from 1976 and 1989 to measure changes. Analyses of ice core data provides a picture of climate history going back 11,700 years, Hardy explains, and the paper reports “clear evidence of surface melting” only near the top.

Hardy says it’s significant that a 160-foot (49-meter) ice core representing nearly 12,000 years of climate history shows bubbles and open voids characteristic of extensive melting and refreezing only in the uppermost (recent) section. “If one accepts that this ice fabric confirms no prior surface melting at any time in the ice-core record, and that the record is really 11,700 years old, this is a very significant finding. However, this first aspect is very difficult to prove, and up until now we have no corroborating dates; our new samples may change this.”

Comparisons of photos taken in 2000 and 2007 with mapping cameras show “dramatic changes,” he and colleagues report. For example, a hole near the center of the Northern Ice Field has grown so much that it seems likely the field will be broken in two in a few years. At the same time, the Furtw?ngler Glacier has shrunk and divided in two. And on this trip Hardy discovered another hole beginning to develop in the Northern Ice Field.

Their new paper presents new ice thickness change calculations, which allows them to make a volume change estimate by comparing data collected in 2000 and in 2007. As Hardy explains, “By establishing a network of stakes on the glacier surfaces, and then repeatedly re-measuring them, I was able to assess how much the glacier thickness changed between 2000 and 2007. Over most measurement intervals the ice thinned, but there were intervals of up to two years when the ice thickness increased, which shows the value of long-term measurements such as these.”

Using these thickness data, he and colleagues established the spatial pattern of net glacier thinning from 2000 to 2007. “So in conjunction with the air photos we could determine how much ice volume was lost to thinning, versus how much was lost to retreat of the vertical walls (area change).”

Before his thickness-change measurements, the only information on glacier thickness had come from old photographs taken by early scientists and climbers. “It doesn’t appear that the glaciers were substantially thicker in the past than they are now, but we can’t precisely quantify this,” says Hardy.

Besides the glacier measurements, last month’s trip yielded three mummified mammals and one bird “just as they emerged from the ice,” says Hardy. He collected small samples for Carbon-14 dating, which will help to precisely reveal the time they died and were buried by snow. These dates will provide an age for the ice surface, and may show that the rate of thinning is increasing.

November 3, 2009.

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