If we want to predict the future of our planet under climate change, we need to better understand what has happened before on Earth, even hundreds of thousands of years in the past.
New research on the Ethiopian highlands during the last glacial period helps to do so. In addition to answering some geological questions, he also posed a new one: What created the gigantic strips of stone on the central Sanetti plateau in the Bale Mountains?
As part of the research, scientists examined samples of moraine pebbles in the Bale and Arsi Mountains, rocks that were formerly said to have been transported by glaciers.
By studying their physical disposition and measuring the extent of decay in a chlorine isotope, they determined that past glaciations would not have been synchronized with other similar stretches of mountains.
(Groos et al., Earth Surface Dynamics, 2021)
“Our results show that the glaciers of the highlands of southern Ethiopia reached their maximum extent between 40,000 and 30,000 years ago, several thousand years earlier than in other mountainous regions of East Africa and the world.” , says glaciologist Alexander Groos of the University of Bern in Switzerland.
Although these highlands are not full of ice today, between 42,000 and 28,000 years ago, thousands of years before the most recent period when ice sheets stretched far from the poles, they would have been crowned by glaciers that they covered up to 350 square miles (approximately 135 square miles). Researchers say relatively early cooling and the appearance of glaciers are likely caused by variations in rainfall and mountain features.
In other words, temperature was not the only engine of glacier movement in East Africa during this time. These ideas can help us understand what can happen next and what the impact is on biodiversity and ecosystems.
As for the massive strips of stone formed by pebbles and basalt columns, they were discovered during the course of the investigation, right in the area of the ancient ice sheet. The stripes are up to 1,000 meters (3,281 feet) long, 15 meters (49 feet) wide and 2 meters (6.5 feet) deep, and have not been seen so far in the tropics.
(Groos et al., Earth Surface Dynamics, 2021)
“The existence of these stone strips on a tropical plateau surprised us, as the so-called periglacial landforms of this magnitude were previously only known from the temperate zone and polar regions and are associated with temperatures of soil around the freezing point, ”says Groos.
Another way in which the Ethiopian highlands are different from their immediate neighbors, in terms of what fell during the last ice age. Scientists think these streaks are the natural result of periodic freezing and thawing of the soil near the ice cap, which would have joined similar rocks.
(Alexander R. Groos / Digital Globe Foundation)
However, this would have required substantial drops in ground and air temperatures, and what is less clear is whether this is typical of the way the high tropical mountains were cooling at the time or whether it was a regional phenomenon.
We will have to wait for future studies from other regions to find out, but the research gives scientists a lot to continue. It is crucial to understand climate change in the tropics: it is where much of the world’s atmosphere and oceans flow from, and it seems that these mountainous regions would have experienced the last glacial period in several different ways.
“Our findings highlight the importance of understanding the local climate context when attempting to extract broader climate interpretations from glacial chronologies,” the researchers conclude in one of their recently published articles.
The research has been published in Scientific advances i Dynamics of the earth’s surface.