Aerial campaign on the Aletsch Glacier
Only superlatives can properly describe the sheer magnitude of the Aletsch Glacier. Measuring over 22 kilometres in length and with a thickness of up to 900 metres, it is the largest glacier in the Alps, accounting for one fifth of Switzerland's total ice mass. But climate change is obviously leaving its mark on the Aletsch Glacier as well. How has the snow cover changed in the Jungfrau-Aletsch region over recent decades? How much mass is the glacier losing each year? At the start of September 2021, a DLR team from the Polar Monitor Project embarked on a two-week mission to seek answers to these and other questions using high-resolution aerial images and a variety of satellite sensors.##markend##
Our journey begins at Jungfraujoch station. At an altitude of 3454 metres, this is Europe's highest railway station. We boarded the electric rack railway at Kleine Scheidegg and took one last awestruck look at the North Face of the Eiger before the train disappeared into the dark tunnel leading to the Jungfraujoch. It is hard to believe that the tunnel through the Eiger and the Mönch was constructed by hand and that it took 16 long years before the railway became operational in 1912.
Arriving at Jungfraujoch, we set off for the Mönchsjoch Hut to rendezvous with our mountain guides. This means we need to ascend another 200 metres, but this time on foot and carrying heavy baggage through the slushy snow. But the stunning view over the Aletsch Glacier makes our efforts worthwhile. We struggle to acclimatise overnight at the hut. "You don't sleep here, you rest," our mountain guide says. Rising from a sleepless night before sunrise, we set off across the glacier to deploy several control points or select prominent objects such as building corners or rain gauges, which will later be used as reference points for the aerial imaging.
The first point proves to be particularly exciting, as we have to cross a bergschrund, a wide crevasse in the glacial ice, in order to survey the rain gauge on a rocky outcrop. We can only hope that the snow bridge, which is only a few centimetres thick, will hold as we cross the deep chasm. Deploying the other control points turns out to be much easier. Roped together and kitted out with crampons, we walk down the glacier and set up more control points at suitable locations. Black and white tarpaulins are laid out and fixed to the snow with spikes, before having their locations measured with centimetric precision using GPS.
By the time almost all the control points have been deployed after a 15-kilometre-trek, we have almost reached our destination, the Konkordia Hut – almost, though, as we still have to climb 467 steps and quite a few metres in altitude. The effects of climate change are particularly noticeable here. When the first hut was built at Konkordiaplatz in 1877, it was situated just a few metres above the glacier. Since then, the Aletsch Glacier has lost so much thickness that the hut is now located on a rocky outcrop – 200 metres above the ice.
On the way back to the Jungfraujoch, we stop at one of the medial moraines to stake out the last control point. Medial moraines behave more or less like conveyor belts. Debris falls onto the ice from the rock faces at the sides of the glacier and is slowly carried towards the valley. Strictly speaking, the Great Aletsch Glacier only forms where the Ewigschneefeld, the Jungfraufirn and the Grosser Aletschfirn converge at Konkordiaplatz. This confluence transforms what are initially lateral scree slopes into the characteristic medial moraines.
The ascent back up to the Jungfraujoch takes some time. From the moment we set off, the Sphinx Observatory sits enthroned on the rocky outcrop of the Jungfraujoch, looking close enough to touch. We are headed for the research station at Jungfraujoch, which is part of the observatory. Many research disciplines are represented here in addition to glaciology, among them the atmospheric sciences, medicine, meteorology and biology.
Eventually, we complete the ascent to the Jungfraujoch but find ourselves bitterly disappointed when an unexpected snowstorm passes over us that evening. Are the control points we attached still visible, or are they buried in snow? We find out the next morning after a reconnaissance flight with the drone; our targets are snowed in. All we can do now is wait and see when the weather will be right for flying.
The research station was built into the rock in 1931. Aside from the rustic sleeping quarters, it has a library that is perfect for working and commands a magnificent view of the Aletsch Glacier. We are grateful for this comfort, because the first scientists at the Jungfraujoch had to dig snow caves below the Mönch to be able to conduct their research.
The Jungfraujoch – an unreal place of contrasts
During the day, tourists from all over the world come to admire the Swiss Alps Jungfrau-Aletsch UNESCO World Heritage Site, walk through the glacier in the Ice Palace or stock up in one of the countless souvenir shops. Over one million visitors flock to the site every year. But silence descends when the last train has departed for the valley in the evening, and the numerous tunnels seem almost ghostly. The former hostel burned down a few decades ago, so only we researchers and the research station’s operations room remain behind. We really enjoy this privilege, especially when the weather is good. Visitors can ride Switzerland’s fastest elevator (111-metre ascent in 25 seconds) to the terrace of the Sphinx Observatory and enjoy breathtaking sunsets to the sound of Alpine horns.
Finally, flying weather arrives – but then …
At 05:00 it is time to get up. Once again, we set off for the Konkordia Hut, this time to clear the snow from the control points. We also need to measure their locations again to determine the speed of the glacier. In addition to the glacier flow velocity, the aerial survey will also provide information on its mass balance. The MACS camera system takes aerial photographs and maps an elevation model, which can be compared with existing elevation models to calculate the decrease in ice thickness. The high-resolution aerial images are used to determine the current snow cover and help to validate DLR's 'Global SnowPack' – a dataset on daily snow cover derived from satellite data.
Arriving at the first control point, we look in astonishment at the misshapen marker. The snow has melted far more beneath the black sections than under the white ones. The reverse of this effect is used in summer by covering glaciers with white tarpaulins to increase the reflection of radiation and reduce melting.
Ground-based reference data on the snow cover is to be collected the next day. This was originally scheduled for the same time as the aerial survey. Sadly, though, the armed forces have blocked the airspace for the next day, which thwarts our plans. Disappointed, we walk back to the research station.
But the wait pays off in the end, and as we calibrate the final control point on the eastern ridge of the Jungfrau, we are rewarded with a magnificent view over the Aletsch Glacier that remains hidden from the majority of visitors. And a glance at the sky is no less pleasing; our aircraft with the MACS camera system is circling above our heads and is finally able to acquire the long-awaited aerial images.