BLOGS

Figure 1. The Vadret da Tschierva glacier in 1935 (top) and in 2022 (bottom).Photos courtesy of swisstopo, L. Hösli, G. Carcanade, M. Huss, VAW-ETHZ.

Topics: Civilization, Climate Change, Fluid Mechanics, Global Warming, Meteorology, Research

Glaciers—dynamic masses of ice descending from the mountain tops—have always been fascinating to humankind. They intrinsically belong to the high-alpine environment. Countless photographs immortalize their bright white beauty and the power they radiate. Glaciers have been depicted on oil and parchment for centuries, as if trying to capture their transience. They are constantly moving; under the influence of gravity, the ice generated at high elevation flows downwards and shapes tremendous glacier tongues that are speckled with deep fissures known as crevasses. Sometimes, the openings to these crevasses are hidden by a light dusting of snow; subsequently, mountaineers need a lot of experience to accurately judge their exposure to the ice.

Even though glaciers are not living things, they are not lifeless. For many mountain regions worldwide, glaciers function similarly to lungs: They absorb snow in wintertime and “breathe” out water during hot summer days. This glacier water is urgently needed, especially in dry periods.

Glaciers consequently have a relevance that goes far beyond the mountain peaks where they reside. A reduction in meltwater from glaciers would be painful for nature and the global economy: irrigation of fields would be restricted, the temperature and mineralization of rivers would change, and during periods of drought, serious bottlenecks could come into existence for the drinking water supply and for shipping on rivers. In addition, melting glacial ice contributes to sea-level rise and therefore directly or indirectly affects billions of people living near the coast.

Despite, or perhaps because of, their majestic appearance, glaciers can also pose an immediate threat. Glaciers can produce floods and ice avalanches that endanger villages in the valleys. Together with permafrost, glaciers also stabilize mountain flanks and therefore reduce the potential for rock falls and landslides—a role that is becoming increasingly lost.

The so-called “eternal” ice of glaciers tells a long and dynamic story. During the Ice Age, ice sheets covered a large part of the North American continent, as well as Europe. The last time this happened was around 20,000 years ago—a blink of the eye from a geological perspective. Since then, the climate has changed, due both to natural factors and to anthropogenic influences—human-caused factors—which have massively accelerated over the past 100 years (Marzeion et al., 2014). As a result, the glaciers are still present, but they are getting smaller every year.

The Alps’ iconic glaciers are melting, but there’s still time to save (most of) the biggest, Matthias Huss, Bulletin of the Atomic Scientists.

Left: the electron density isosurface from theoretical DFT calculations. S and W atoms are shown in yellow and blue respectively. Right: transmission electron microscopy image. Courtesy: R Boya

Topics: Fluid Mechanics, Materials Science, Nanofluidics, Nanotechnology

Gases flow through a porous membrane at ultrahigh speeds even when the pores’ diameter approaches the atomic scale. This finding by researchers at the University of Manchester in the UK and the University of Pennsylvania in the US shows that the century-old Knudsen description of gas flow remains valid down to the nanoscale – a discovery that could have applications in water purification, gas separation, and air-quality monitoring.

Gas permeation through nano-sized pores is both ubiquitous in nature and technologically important explains Manchester’s Radha Boya, who led the research effort along with Marija Drndić at Pennsylvania. Because the diameter of these narrow pores is much smaller than the mean free diffusion path of gas molecules, the molecules’ flow can be described using a model developed by the Danish physicist Martin Knudsen in the early decades of the 20^th century. During so-called Knudsen flow, the diffusing molecules randomly scatter from the pore walls rather than colliding with each other.

Until now, however, researchers didn’t know whether Knudsen flow might break down if the pores become small enough. Boya, Drndić, and colleagues have now shown that the model holds even at the ultimate atomic-scale limit.

Gas flows follow conventional theory even at the nanoscale, Isabelle Dumé, Physics World