Ground-breaking discovery finally proves rain really can move mountains


Date:
October 16, 2020
Source:
University of Bristol
Summary:
A pioneering technique which captures precisely how mountains
bend to the will of raindrops has helped solve a long-standing
scientific enigma.



FULL STORY ==========================================================================
A pioneering technique which captures precisely how mountains bend to the
will of raindrops has helped to solve a long-standing scientific enigma.


==========================================================================
The dramatic effect rainfall has on the evolution of mountainous
landscapes is widely debated among geologists, but new research led
by the University of Bristol and published today in Science Advances,
clearly calculates its impact, furthering our understanding of how peaks
and valleys have developed over millions of years.

Its findings, which focused on the mightiest of mountain ranges --
the Himalaya -- also pave the way for forecasting the possible impact
of climate change on landscapes and, in turn, human life.

Lead author Dr Byron Adams, Royal Society Dorothy Hodgkin Fellow at the university's Cabot Institute for the Environment, said: "It may seem
intuitive that more rain can shape mountains by making rivers cut down
into rocks faster.

But scientists have also believed rain can erode a landscape quickly
enough to essentially 'suck' the rocks out of the Earth, effectively
pulling mountains up very quickly.

"Both these theories have been debated for decades because
the measurements required to prove them are so painstakingly
complicated. That's what makes this discovery such an exciting
breakthrough, as it strongly supports the notion that atmospheric and
solid earth processes are intimately connected." While there is no
shortage of scientific models aiming to explain how the Earth works,
the greater challenge can be making enough good observations to test
which are most accurate.



==========================================================================
The study was based in the central and eastern Himalaya of Bhutan and
Nepal, because this region of the world has become one of the most
sampled landscapes for erosion rate studies. Dr Adams, together with collaborators from Arizona State University (ASU) and Louisiana State University, used cosmic clocks within sand grains to measure the speed
at which rivers erode the rocks beneath them.

"When a cosmic particle from outer space reaches Earth, it is likely to
hit sand grains on hillslopes as they are transported toward rivers. When
this happens, some atoms within each grain of sand can transform into
a rare element. By counting how many atoms of this element are present
in a bag of sand, we can calculate how long the sand has been there,
and therefore how quickly the landscape has been eroding," Dr Adams said.

"Once we have erosion rates from all over the mountain range, we can
compare them with variations in river steepness and rainfall. However,
such a comparison is hugely problematic because each data point is very difficult to produce and the statistical interpretation of all the data together is complicated." Dr Adams overcame this challenge by combining regression techniques with numerical models of how rivers erode.

"We tested a wide variety of numerical models to reproduce the observed
erosion rate pattern across Bhutan and Nepal. Ultimately only one model
was able to accurately predict the measured erosion rates," Dr Adams said.



========================================================================== "This model allows us for the first time to quantify how rainfall affects erosion rates in rugged terrain." Research collaborator Professor
Kelin Whipple, Professor of Geology at ASU, said: "Our findings show
how critical it is to account for rainfall when assessing patterns of
tectonic activity using topography, and also provide an essential step
forward in addressing how much the slip rate on tectonic faults may
be controlled by climate-driven erosion at the surface." The study
findings also carry important implications for land use management, infrastructure maintenance, and hazards in the Himalaya.

In the Himalaya, there is the ever-present risk that high erosion rates
can drastically increase sedimentation behind dams, jeopardising critical hydropower projects. The findings also suggest greater rainfall can
undermine hillslopes, increasing the risk of debris flows or landslides,
some of which may be large enough to dam the river creating a new hazard
-- lake outburst floods.

Dr Adams added: "Our data and analysis provides an effective tool for estimating patterns of erosion in mountainous landscapes such as the
Himalaya, and thus, can provide invaluable insight into the hazards that influence the hundreds of millions of people who live within and at the
foot of these mountains." The research was funded by the Royal Society,
the UK Natural Environmental Research Council (NERC), and the National
Science Foundation (NSF) of the US.

Building on this important research, Dr Adams is currently exploring
how landscapes respond after large volcanic eruptions.

"This new frontier of landscape evolution modelling is also shedding
new light on volcanic processes. With our cutting-edge techniques to
measure erosion rates and rock properties, we will be able to better
understand how rivers and volcanoes have influenced each other in the
past," Dr Adams said.

"This will help us to more accurately anticipate what is likely to happen
after future volcanic eruptions and how to manage the consequences for communities living nearby."

========================================================================== Story Source: Materials provided by University_of_Bristol. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. B. A. Adams, K. X. Whipple, A. M. Forte, A. M. Heimsath and
K. V. Hodges.

Climate controls on erosion in tectonically active
landscapes. Science Advances, 2020 DOI: 10.1126/sciadv.aaz3166 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201016143049.htm

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