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If we are to predict the future of our planet under climate change, we need to better understand what has happened on Earth before, even hundreds of thousands of years in the past.
New research in the Ethiopian highlands during the last ice age is helping to do just that. In addition to answering some geological questions, he also raised a new one: what created the gigantic bands of stone on the central Sanetti plateau in the Bale mountains?
As part of the research, scientists looked at samples of boulder moraine in the Bale and Arsi mountains, rocks that would once have been washed away by glaciers.
By studying their physical layout and measuring the extent of the decay of an isotope of chlorine, they determined that past glaciations would not have been synchronized with other similar expanses of mountains.
(Groos et al., Earth Surface Dynamics, 2021)
“Our results show that glaciers in the southern highlands of Ethiopia reached their maximum extent between 40,000 and 30,000 years ago, several thousand years earlier than in other mountainous regions of Africa. East and around the world, ”explains glaciologist Alexander Groos from the University of Bern in Switzerland.
Although these highlands are not ice-filled today, between 42,000 and 28,000 years ago – thousands of years before the most recent period in which the ice caps stretched far from the poles – they would have been topped by glaciers that covered up to 350 squares. kilometers (approximately 135 square miles). The relatively early cooling and the appearance of glaciers are likely caused by variations in precipitation and mountain characteristics, the researchers say.
In other words, temperature was not the only driver of glacier movement across East Africa during this time. Such information can help us understand what might happen next and what the impact will be on biodiversity and ecosystems.
As for the massive stone bands formed by boulders and basalt columns, they were discovered during research just outside the area of the ancient ice cap. The bands are up to 1,000 meters (3,281 feet) long, 15 meters (49 feet) wide and 2 meters (6.5 feet) deep, and have never been seen before in the tropics.
(Groos et al., Earth Surface Dynamics, 2021)
“The existence of these stone bands on a tropical plateau surprised us, because the so-called periglacial reliefs of this magnitude were previously only known from the temperate zone and the polar regions and are associated with ground temperatures around the point. freezing, ”says Groos.
Another way the Ethiopian highlands are then different from their immediate neighbors, in terms of what happened during the last ice age. Scientists believe these scratches are the natural result of the periodic freezing and thawing of the ground near the ice cap, which would have pulled similar rocks together.
(Alexander R. Groos / Digital Globe Foundation)
This would, however, have required substantial drops in both soil and air temperatures – and what is less clear is whether this is typical of how high tropical mountains cooled at the time, 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 a lot to continue. Understanding climate change in the tropics is crucial – this is where much of the circulation of the world’s atmosphere and oceans originates from – and it looks like these mountainous regions may have experienced the last ice age in different ways. .
“Our results underscore the importance of understanding the local climatic context when attempting to derive broader climatic interpretations from glacial chronologies,” the researchers conclude in one of their recently published papers.
The research was published in Scientific progress and Earth’s surface dynamics.
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