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(Groos et al., Earth Surface Dynamics, 2021) |
If we want to foresee the future of our world in the face of
climate change, we need to know more about what has happened on Earth in the
past, perhaps hundreds of thousands of years.
This is something that new research into the Ethiopian
Highlands during the Last Glacial Period will help with. It has not only
answered several geological questions, but it has also prompted a new one: What
caused the massive stone stripes that run across the Bale Mountains' central
Sanetti Plateau?
Scientists examined moraine boulder samples in the Bale and
Arsi Mountains, rocks that would have been brought along by glaciers in the
past.
They determined that previous glaciations may not have been
in line with other adjacent stretches of mountains by observing their physical
arrangement and calculating the degree of decay in a chlorine isotope.
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(Groos et al., Earth Surface Dynamics, 2021) |
According to glaciologist Alexander Groos of the University
of Bern in Switzerland, glaciers in the southern Ethiopian Highlands peaked
between 40,000 and 30,000 years ago, thousands of years earlier than in other
mountainous regions in Eastern Africa and around the world.
Although the highlands aren't covered in ice today, they
were topped by glaciers that covered up to 350 square kilometers between 42,000
and 28,000 years ago - thousands of years before the most recent time in which
ice sheets extended far from the poles (about 135 square miles). Variations in
rainfall and mountain features are likely to blame for the early cooling and
onset of glaciers, according to the researchers.
To put it another way, temperature wasn't the only factor
driving glacier movement in Eastern Africa at the time. Such knowledge will
help us foresee what will happen next and what effects it will have on
biodiversity and ecosystems.
The massive stone stripes created by boulders and basalt
columns were discovered during the research process, just outside the former
ice cap's location. The stripes, which can be 1,000 meters (3,281 feet) long,
15 meters (49 feet) wide, and 2 meters (6.5 feet) deep, have never been seen in
the tropics before.
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(Groos et al., Earth Surface Dynamics, 2021) |
We were surprised to find these stone stripes on a tropical
plateau because periglacial landforms of this scale have traditionally only
been found in the temperate zone and the Polar Regions, and are correlated with
ground temperatures near freezing point, according to Groos.
In terms of what occurred during the last ice age, the
Ethiopian Highlands vary from their immediate neighbors in another way. These
streaks are thought to be the result of frequent freezing and thawing of the ground
near the ice cap, which would have drawn similar rocks together.
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(Alexander R. Groos/Digital Globe Foundation) |
However, significant drops in ground and air temperatures
would have been expected – and it's unclear if this was typical of how tropical
high mountains cooled at the time, or if it was a regional phenomenon.
We'll have to wait for further studies from other regions to
find out, but the research offers plenty of knowledge for scientists to work
with. Understanding climate changes in the tropics is important because it is
from here that much of the world's atmosphere and oceans flow, and it appears
that these mountainous areas may have undergone the Last Glacial Period in a
variety of ways.
In one of their recently published articles, the researchers
write, "Our findings illustrate the significance of recognizing the local
climatic setting when attempting to draw broader climatic interpretations from
glacial chronologies."
The research has been published in Science Advances and
Earth Surface Dynamics.
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