If we want 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 on the Ethiopian highlands during the last ice age helps to do just that. In addition to answering some geological questions, it also created a new question: what created the gigantic rock stripes over the central Sanetti plateau in the Bale Mountains?
As part of the research, scientists looked at moraine rock samples in the Bale and Arsi Mountains, rocks that would once have been carried along by glaciers.
By studying their physical arrangement and measuring the degree of decay in an isotope of chlorine, they determined that glaciation would not be consistent with other similar mountains.
(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, a few thousand years earlier than in other mountainous regions in East Africa and worldwide,” says glacier 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 in which ice sheets stretched far from the poles – they would have been covered by glaciers that covered as many as 350 square feet. kilometers (about 135 square miles). The researchers say the relatively early cooling and onset of the glacier is likely caused by rainfall and mountain features.
In other words, temperature was not the only driver of glacier movement in East Africa during this time. Such insights can help us understand what might happen next, and what the impact on biodiversity and ecosystems is likely to be.
What formed the massive rock stripes through rocks and basalt columns was discovered in the course of research, just outside the area of the former ice sheet. The stripes are up to 1000 meters (3,281 feet) long, 15 meters (49 feet) wide and 2 meters (6.5 feet) deep and have not been seen in the tropics before.
(Groos et al., Earth Surface Dynamics, 2021)
“The existence of these rocky stripes on a tropical plateau surprised us, because so-called periglacial landforms of this magnitude were previously known only from the temperate zone and polar regions and are related to soil temperatures around the freezing point,” says Groos.
Another way the Ethiopian Highlands is different from their immediate neighbors in terms of what went down during the last ice age. The scientists think that these stripes are the natural consequence of periodic freezing and thawing of the soil near the ice sheet, which would cause similar rocks to converge.
(Alexander R. Groos / Digital Globe Foundation)
However, this would have required a significant drop in ground and air temperatures – and what is less clear is whether this is typical of the way tropical high mountains cooled at the time, or that it was a regional phenomenon.
We will have to wait until future studies from other regions find out, but the research gives scientists enough to go on. The understanding of climate change in the tropics is crucial – this is where much of the world’s atmosphere and oceans spread – and it would seem that these mountainous regions could have experienced the last glacial period in different ways.
“Our findings highlight the importance of understanding the local climate environment as we try to draw broader climate interpretations from glacial chronologies,” the researchers conclude in one of their recently published articles.
The research was published in Scientific progress and Earth Surface Dynamics.