A recent storm brought to light flint scrapers and arrowheads dating from the Palaeolithic era in a Schaffhausen forest.

The flints examined by the Schaffhausen Archaeological Service were discovered in a forest [Credit: Township of Schaffhausen]

The Stone Age tools were found by a jogger among the roots of a tree felled by strong winds a month ago and immediately reported his discovery to the Cantonal Archaeological Service.

Archaeologists have since been able to extract many other finely worked stone objects from the site.

"12,000 years ago, small groups of hunter-gatherers occupied this area which today is heavily forested but was then only a sparse landscape of birch and pine trees," explained the Cantonal Archaeological Service, adding that "the stone used for the flint came from the Schaffhausen high plateau of the Randen."

"At the scene of the find, hunter-gatherers fashioned spearheads for reindeer hunting and tools to work furs. This is evidenced by a large amount of waste and a few finished products."

Source: Swissinfo [February 06, 2018]

ETH researchers have identified a rock glacier in canton Valais that is degrading and moving very quickly. Fortunately, it does not present an immediate threat to people and infrastructure.

Nothing stands still for long here: measurement station on the rock glacier at the foot of the Furggwanghorn mountain [Credit: Thomas Buchli/ETH Zurich]

Rock glaciers, containing ice and rock debris as alpine permafrost, are changing rapidly and profoundly in response to climate change. They create the risk of mass movements as they creep downhill, subside, spread and sometimes collapse. The question is whether these glaciers can potentially pose a threat to the surrounding area, including local residents and infrastructure.

To answer this question, researchers from a number of ETH institutes, and from the ETH spin-off Terrasense, have carried out a detailed study of a rock glacier situated at the foot of the Furggwanghorn mountain in the Turtmann Valley, in the canton of Valais. Their study has just been published in the journal Permafrost and Periglacial Processes.

"To identify the potential threat, you first need to ascertain the state of the rock glacier, and understand how it behaves," says Thomas Buchli, a former doctoral researcher in the Chair of Geotechnical Engineering at ETH Zurich. "There are still some gaps in our knowledge here."

Although many studies exist on rock glaciers, scientists have generally focused on measuring their surface and internal temperatures, as well as their surface creep rates. "The interaction between the soil mechanics, the ground temperature and the water inside a rock glacier has never been investigated in such detail," Buchli emphasises. Different measurements must be combined to achieve this. Most research to date has been limited to aspects such as temperature or surface movements, and this information has been compared with other rock glaciers. But these comparisons are not always helpful for understanding an individual rock glacier.

When writing his dissertation, the geotechnical engineer Buchli collaborated with geophysicists, hydrologists and geologists, using an impressive arsenal of measuring and monitoring equipment that was positioned on and near the Furggwanghorn rock glacier.

The surface of the rock glacier pictured on the left in the canton of Valais is changing rapidly as it moves downhill at a steadily increasing pace [Credit: ETH Zurich]

Among other things, the researchers used radar and laser measuring devices to characterise the surface. With the help of GPS, they also determined the surface creep velocity of the rock glacier. To investigate the structure of the ground, the temperature and water content, as well as the internal creep rates, the engineers bored several holes up to 30 metres deep into the permafrost. They inserted thermistors to measure the temperature and also novel inclinometers in these boreholes. Some of the measurements were unique: in one borehole, for example, Buchli was able to detect for the first time continuous creep movements by the rock glacier of up to three metres. The researchers gained additional information on the stratification and structure of the rock glacier with geophysical investigations.

By linking the data together, the researchers were able to obtain a uniquely detailed picture and a ground model that helped to explain the rock glacier's behaviour.

It was striking how quickly and powerfully the surface of the rock glacier moved and changed during the investigation period. Scientists already knew that the Furggwanghorn rock glacier is warming and degrading faster than the majority of other rock glaciers. "Even so, I was surprised by the speed," says Buchli. "Tilting, twisting, subsiding –everything on the rock glacier was somehow in constant motion."

However, the rock glacier did not move as one mass, but in sections. It moved downhill over several metres per year in one part of the frontal area, while the movement in its accumulation zone was only a few decimetres and it was entirely static in another part of the front section.

The surface of the rock glacier showing zones with different creep velocities [Credit: Thomas Buchli/ETH Zurich]

Various factors can be considered as drivers of these changes: rainfall, warming air temperatures, water content and of course the temperature and composition of the permafrost. "There are many factors controlling a rock glacier. Isolating just one of them is difficult," says Buchli.

"The Furggwanghorn rock glacier is also relatively warm," the geotechnical engineer says. At the beginning of the measurements, the temperatures in the core of the permafrost were slightly below freezing point. Surface water does not necessarily freeze and flows through a system riddled with pores and cracks. If the permafrost was colder, the water would turn to ice. This permafrost would contain a more continuous ice phase, and hence be stronger and less permeable.

The temperatures rose continuously in the permafrost during the six years of measurements. They are currently barely above zero in large areas of the rock glacier.

"Already during drilling, we realised that the rock glacier had to be relatively warm, because the drill head kept encountering places with free water," Buchli recalls.

Water flowing through the rock glacier should also be responsible for some of the surface deformations, he says. Water transports heat from the outside into the rock glacier. The permafrost thaws, and causes subsidence in the ground above. However, the researchers have not yet fully understood how the water flows through the rock glacier. "The water flow through a rock glacier is very complex and difficult to investigate," Buchli says.

The researchers could not find any immediate danger for the area below – in this case, the Turtmann valley. It is more likely that the rock glacier, or parts of it, will quietly subside, leaving unfrozen debris behind. "These could trigger a debris flow during very heavy rainfall in the worst-case scenario and then pose a very real threat," says Buchli. In the case of the Furggwanghorn rock glacier, however, the researchers have not found any evidence of a development in this direction. Even so, rock glaciers still require constant monitoring.

Author: Pe­ter Rüegg | Source: ETH Zurich [January 25, 2018]

Rock avalanches and torrents started to form V-shaped valleys in the Swiss Alps approximately 25 million years ago. This landscape contrasts to the flat and hilly scenery, which characterized the Alps a few millions of years before. Geologists from the University of Bern applied digital technologies to unravel these changes in landscape evolution. They analysed 30 to 25 million-year old lithified rivers in Central Switzerland and came out with a detailed picture of how the Alps evolved within a short time interval.

Mount Rigi, picture taken from the front. The number of lithified river deposits increase towards the top of the mountain  range. The pebble sizes increase from the base to the top of Mount Rigi. The river, which deposited these rocks,  adapted a chaotic flow pattern through time [Credit: Philippos Garefalakis, University of Bern]

The current shape of the Alps with steep V-shaped valleys and torrents have evolved during approximately five millions of years. This time span might be perceived as very long, but it is a few seconds for geologists. This was the major outcome of a study by Philippos Garefalakis and Fritz Schlunegger from the University of Bern, Switzerland, who analysed thousands of pebbles at Mount Rigi situated in Central Switzerland.

This mountain, which has been considered by Goethe as the Queen of the Mountains, because of its spectacular view, consists of lithified rivers with pebbles. These rocks have been transported by the Alpine rivers in the geologic past, and they document the rise of the Alps and the related change of the landscape. The scientists found out that the Central Swiss Alps evolved from British-type of hillslopes and flats to a rugged region with torrents and deep gorges. The results of their study have recently been published by the Nature-Group in Scientific Reports.

From a meadow countryside to the Alpine landscape

30 million years ago, the headwaters of the Alpine rivers were situated on a plateau with flat hillslopes, similar to what we currently find in Great Britain. "The leisurely streams deposited tons of pebbles, which resulted in a stack of thousands of lithified rivers, referred to as conglomerates," explains Philippos Garefalakis, the senior author of the published article. "Accordingly, each bed represents the deposits of a river back in geologic times."

Headwaters of Alpine streams approximately 30 million years ago (left) with an Alpine plateau and a meadow countryside.  The handcraft on the right side illustrates the landscape of the Alps at 25 million years before present with steep valleys  where torrents originated [Credit: Philippos Garefalakis, University of Bern]

Philippos and his team analysed bed by bed and thousands of pebbles from the base to the top of Mount Rigi. The changes surprised the scientist. "The 30 million-year old deposits at the base of Mount Rigi contain pebbles that have the size of an apple, and the streams were 2-4 meters deep. On top of the mountain range, the 25 million-year old sediments expose boulders as large as a football, and torrents were less than 1 meter deep." The Alpine streams must have gained in power, and they adapted a chaotic flow pattern.

Dramatic evolution

"The change in the Alpine landscape must have been dramatic and fast," explains Philippos and looks toward the Alps, which are clearly visible from Bern on a sunny day like this. "Boulders as large as a football can only be entrained by strong torrents during floods." These processes are typical in a steep landscape where rock avalanches and landslides supply large volumes of boulders and material. The Alps thus had their current shape as early as 25 million years ago.

The investigated rocks beneath the summit of Mount Rigi. Pebbles as large as footballs imply that the Alpine rivers had  the character of a torrent. The rocks at Mount Rigi thus document the occurrence of a large delta that formed  at the border of the Alps 25 million years ago [Credit: Philippos Garefalakis, University of Bern]

The situation, however, was different 30 million years ago. Streams were smooth and had their headwaters in a meadow countryside, which characterized the Alps at that time. "These changes occurred as the Alps started to rise and to steepen, which occurred -- for geological standards -- within a short time interval."

Application of digital technologies

Engineers have disclosed quantitative relationships between the size of gravels in rivers and stream power. "We can apply the identical concepts to stream deposits of the geologic past, but we need to measure the size of thousands of pebbles," says Philippos. This was only possible thanks to computer technologies, which allows to measure a large number of pebbles on digital photographs. This new technology has been applied for the first time to rocks and will yield new insights about our streams on Earth in the geological past.

Source: University of Bern [January 09, 2018]