Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Dwarf Dunes Record Climate History in Desert Sand

03.05.2018

Wind-driven sand is understood to create ripples on a centimetre scale and dunes spanning tens of metres, but so-called megaripples of intermediate size have remained puzzling. A theory of aeolian sand sorting now fills the gap, suggesting that megaripples and similar structures seen on Mars might hold encrypted records of the local climate history.

Sandy deserts aren't smooth. Like water surfaces, they are decorated by tiny surface ripples and much larger waves, called dunes, excited by turbulent winds. Now, writing in Nature Physics, an international team of geomorphologists and physicists elucidates the physical mechanism creating a third type of sand wave, with no marine analogy.


Unexpected relationship: Megaripples and sand dunes

Foto: Dr. Hezi Yizhaq

These curious “megaripples” resemble large ripples but have long eluded a mechanistic understanding and clear phenomenological characterization. Not surprisingly—the authors say—as they are actually dwarf dunes.

The new perspective might be key to deciphering their morphological long-term memory of ambient soil and weather conditions, and provide interesting new directions for geomorphological analysis and remote sensing applications to related bedforms seen on Mars, for example.

The starting point of the study was a closer look at the conditions under which megaripples form. Turbulent winds not only create sand waves, they also sort grains by size. Fine grains advance quickly while coarser grains trail behind. For this reason, sand found in large dune fields—having been transported for miles by the wind—is typically composed of grains that are all about the same size.

In contrast, megaripples contain grains of all different sizes. Under erosive conditions, the fine grains leave while coarser grains, which are too heavy to be mobilized by the wind, gradually accumulate on the sand bed.

This sets off a special bimodal transport process, in which the impact of high flying fine grains helps the coarse grains to advance in tiny steps. Their drastically reduced hop length prompts a corresponding downsizing of the dunes they form.

As Marc Lämmel et al. now demonstrate, this new interpretation of megaripples as mini-dunes of coarse grains is supported not only by the known co-localization of megaripples and coarse grains. It is quantitatively corroborated by close morphological and dynamical similarities between megaripples and ordinary sand dunes, which had remained unnoticed because of the enormous difference in size.

An important implication of the new work is that megaripples are extraordinarily sensitive to fluctuations in grain-size and wind-strength. It explains why megaripples stop growing during periods of weak winds and quickly erode during storms. What has plagued systematic field studies in the past, now renders megaripples perfect candidates for retrodicting past weather and climate conditions.

How their morphology and grain composition encodes records of past sorting and growth phases reminds one of the growth rings in tree trunks. If judiciously interpreted, petrified or extraterrestrial megripples,
say, will reveal valuable information about the climate history.

While further research is needed to establish a reliable routine for deciphering the messages in the sand, nothing prevents you anymore from embarking on this endeavor yourself, equipped with spade and sieve, on your next beach or desert trip. Before you set off, here is the portable version of the theory for analyzing your data: megaripples are mini-dunes of mega-grains making mini-jumps.

ORIGINAL PUBLICATION:
Marc Lämmel, Anne Meiwald, Hezi Yizhaq, Haim Tsoar, Itzhak Katra, and
Klaus Kroy:

"Aeolian sand sorting and megaripple formation"
Nature Physics (2018) Advance Online Publication (AOP)

Contact:
Prof. Dr. Klaus Kroy
Institute for Theoretical Physics, Leipzig University, Germany
Telefon: +49 341 97-32436
E-Mail: klaus.kroy@itp.uni-leipzig.de

Weitere Informationen:

https://www.nature.com/articles/s41567-018-0106-z

Susann Huster | Universität Leipzig
Further information:
http://www.uni-leipzig.de

More articles from Earth Sciences:

nachricht Massive impact crater from a kilometer-wide iron meteorite discovered in Greenland
15.11.2018 | Faculty of Science - University of Copenhagen

nachricht The unintended consequences of dams and reservoirs
14.11.2018 | Uppsala University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: UNH scientists help provide first-ever views of elusive energy explosion

Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.

Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

European Space Talks: Weltraumschrott – eine Gefahr für die Gesellschaft?

23.10.2018 | Event News

 
Latest News

Purdue cancer identity technology makes it easier to find a tumor's 'address'

16.11.2018 | Health and Medicine

Good preparation is half the digestion

16.11.2018 | Life Sciences

Microscope measures muscle weakness

16.11.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>