A new study reveals that rocky glaciers, which hide huge amounts of ice inside them under layers of rock and debris, may represent a massive water reservoir that is not visible to the naked eye.
Rock glaciers differ from traditional glaciers, which appear as vast white expanses of ice. They consist of a mixture of ice and rock, and are covered by a thick layer of rock debris that makes the ice inside almost invisible from the surface.
There are more than 51,000 documented rock glaciers around the world, including more than 10,000 in the United States.
The importance of these formations lies in their ability to retain ice for extended periods, as the overlying rocky cover acts as an insulating layer, protecting the ice from sunlight and heat. However, this same cover makes it difficult for scientists to determine the exact amount of ice present within them.
To overcome the difficulty of measuring the ice that lies beneath the rocks, University of Utah glaciologist Leif Anderson and his team studied the Timpanogos Glacier at the foot of Mount Timpanogos in Utah, and used it as a model to develop a new method for estimating the volume of ice inside rocky glaciers.
Scientists usually use ground-penetrating radar to study glaciers, but this technique does not work as efficiently with rocky glaciers, because the rocks and debris mixed with the ice scatter the radio waves, making it difficult to obtain clear images of the internal structure.
Therefore, scientists resorted to gravity measurement, a technique that allows them to detect differences in density beneath the Earth's surface. This is because ice is much less dense than the surrounding rock, resulting in a decrease in the acceleration due to gravity over areas with greater ice content.
"There is a huge density difference between the rocks that make up Mount Tempanogos and the very low-density ice in the adjacent rocky glacier," said Michael Thorne, a geophysicist and co-author of the study.
He added: "When we measure the acceleration due to gravity over a rocky glacier, we observe a greater decrease in this acceleration the more we take measurements over areas with thicker ice."
The team conducted 232 measurements at various locations around the Tempanogos Glacier, then used statistics and modeling techniques to transform this data into a three-dimensional model that illustrates the glacier's shape, thickness, and internal structure
The results showed that the Tempanogos Glacier consists of about 83% ice and 17% rock debris by volume, with an average ice thickness of about 18.8 meters.
Scientists estimate that the glacier contains a total of about 1.5 million cubic meters of ice, an amount roughly the size of the Great Pyramid of Giza, or about 600 Olympic swimming pools.
This ice weighs approximately 1.4 million tons, and it is a huge water reservoir that is hidden almost entirely under the rock cover.
By utilizing data from previous studies that examined the internal structure of rock glaciers, scientists were able to use the surface area of these formations to estimate the amount of ice inside them, a method that can be applied to wider areas without the need to conduct a detailed survey of each rock glacier.
By applying this method to documented rock glaciers, scientists estimated that the state of Utah contains about one billion metric tons of ice distributed across 836 rock glaciers.
In the western United States, the ice stockpile is estimated at about 12 billion tons, while the total ice stored within rocky glaciers around the world reaches about 48 billion tons.
The team believes that determining the size of this reservoir has become increasingly important as temperatures continue to rise and glaciers change behavior. Some traditional glaciers may transform into debris-covered glaciers, and then into glacial rock formations, making it essential to understand the amount of water they store.
Some rocky glaciers can also become unstable during periods of warming, which could pose risks to downstream areas and infrastructure.
The results of the study were published in the Journal of Geophysical Research: Earth's Surface.
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