If we are to predict the future of our planet under climate change, we need to better understand what happened on Earth before, even hundreds of thousands of years in the past.
New research into the Ethiopian highlands during the last ice age is helping. In addition to answering some geological questions, it has also raised a new one: what created the giant stone streaks across the central Sanetti Plateau in the Bale Mountains?
As part of the study, scientists looked at samples of moraine boulders in the Bale and Arsi Mountains, rocks that are said to have once been carried by glaciers.
By studying their physical arrangement and measuring the rate of decay in an isotope of chlorine, they determined that earlier ice ages would be out of sync with other similar mountainous regions.
(Groos et al., Earth Surface Dynamics, 2021)
“Our results show that glaciers in the southern Ethiopian highlands reached their maximum extent between 40,000 and 30,000 years ago, several thousand years earlier than in other mountain regions in East Africa and worldwide,” said glaciologist Alexander Groos of the University of Bern in Switzerland. .
Although these highlands are not filled with ice today, between 42,000 and 28,000 years ago – thousands of years before the most recent period when ice sheets extended far from the poles – were said to have been covered by glaciers covering a staggering 350 square meters. kilometers (about 135 square miles). The relatively early cooling and onset of the glacier is likely caused by variations in rainfall and mountain features, the researchers say.
In other words, temperature was not the only driver of glacier movement across East Africa during this period. Such insights can help us understand what can happen next and what the impact on biodiversity and ecosystems is likely to be.
As for the massive stone streaks formed by boulders and basalt columns, these were discovered during the investigation, just outside the area of the former ice sheet. The stripes are up to 1000 meters long, 15 meters wide and 2 meters deep and have never been seen in the tropics before.
(Groos et al., Earth Surface Dynamics, 2021)
“The existence of these stone stripes on a tropical plateau surprised us, as so-called periglacial landforms of this magnitude were previously known only from the temperate zone and polar regions and are associated with soil temperatures around freezing,” says Groos.
Another way that the Ethiopian Highlands are different from their immediate neighbors, in terms of what happened during the last Ice Age. The scientists believe these streaks are the natural result of periodic freezing and thawing of the soil near the ice sheet, which would have pulled similar rocks together.
(Alexander R. Groos / Digital Globe Foundation)
However, that would have required a significant drop in ground and air temperatures – and what’s less clear is whether this is typical of the way tropical high mountains cooled back then, or if it was a regional phenomenon.
We’ll have to wait for future studies from other regions to find out, but the research gives scientists enough to move forward. Understanding climate change in the tropics is crucial – it’s where much of the circulation of the world’s atmosphere and oceans comes from – and it appears that these mountainous regions experienced the last Ice Age in different ways.
“Our findings emphasize the importance of understanding the local climatic environment when trying to draw broader climatic interpretations from glacial chronologies,” the researchers conclude in one of their newly published papers.
The research is published in Science Advances and Dynamics of the Earth’s surface