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Need more information for a safe city

Professor Hanne Christiansen is the head of the Arctic Geology department at The University Centre in Svalbard. She says that when landslides occurred there was 18 millimeters of rain with an intensity of up to 2.8 millimeters per hour over a 12-hour period. This happened while the landscape had its maximum thawing depth and after a very wet summer with 138 millimeters of rain since June 1. FOTO: Ole Humlum

Need more information for a safe city

UNIS geologists believe, among other things, monitoring stations must be established that can help predict when landslides may threaten the city.

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22.10.2016 kl 13:24

When an emergency alert about heavy rain in Longyearbyen was sent out before last weekend, Kjersti Olsen Ingerø, head of the technical sector for Longyearbyen's municipal government, contacted The University Centre in Svalbard.

"We ordered a report documenting how nature was handling the rainfall with the underlaying conditions when the weather hit," Ingerø said.

She said the city is working to form a foundation so that in the future officials will be better at predicting what might happen.

The report was ready Wednesday and was written by a group of geologists at UNIS. They observed several landslides and debris flows in the Longyearbyen area. Some were small, while several debris flows came down in the lowlands of the hillsides. A landslide next the cemetery was huge in the context of Svalbard.

"It moved up to 5,000 cubic meters of the mountainside toward the road and down towards Longyearelva," said Hanne Christiansen, a professor at UNIS.

The last landslide of that size was in the summer of 1972, when several landslides came down to the city.

Need more data

Based on landslides over the weekend, not to mention the avalanche last Dec. 19, Christiansen said she believes there is a need for measuring stations providing hourly readings of precipitation, snow depth, water content and temperature of the ground down to the permafrost.

Such data is necessary for the best assessment of potential avalanches, landslides and debris flows.

Before the rain last weekend, UNIS geologists put out their own rain gauges that could provide data on rainfall intensity minute by minute.

"Being able to calculate precipitation intensity appears to be important for when a landslide might eventually go," Christiansen said.

The professor also said there must be a discussion about ways to collect, process and share data from such stations to the public for monitoring, educational and research purposes. Through it Longyearbyen can develop a system for modeling various slope processes, which can be used when making decisions about public safety. In addition, people will learn more about how the Svalbard landscape responds to heavy precipitation in different seasons.

With the NVE's report
The Norwegian Water Resources and Energy Directorate (NVE) is scheduled to complete its report assessing avalanche risks in Longyearbyen.

"It will describe such types of events that we have had," said Knut Ivar Aune Hoseth, who works for NVE's landslide and water resources division in the northern region. "That the landslide happened during the weekend is also useful to get an overview of what could be a threat in the future."

He said that they, along with city and The Governor of Svalbard, have started work to determine how buildings can be secured. There are two possible solutions. One is to prevent avalanches from reaching the settlement through a notification system or permanent safeguards. The second is to move buildings that may be exposed to avalanches.

Avalanche warnings underway
The NVE activated its warning system for snow and slush avalanches in Longyearbyen for the season on Tuesday.

"We have no basis yet to alert in terms of the floods or landslides other than on a general basis," Hoseth said. "It is important to gain more experience and knowledge, and ensure its use in the future.".

He said they have not yet been in contact with UNIS in terms of flooding and landslides.

"There we have yet another way to go, but when it comes to avalanche warnings we have benefitted from UNIS activity," Hoseth said. "I think it would be positive to use local expertise also in terms of soil and debris flows. So we are now taking the initiative to have more exchanges of experiences between the mainland and Svalbard."

Følger fortløpende
The road between the old museum and Huset was closed Saturday morning after landslide from Platåberget spilled across the road. The same day the road into Endalen was also closed. One of governor's rescue helicopter flew over Longyearelva to see if there were blockages that might cause flooding. It also flew over the side valleys of Longyearbyen to see if there had been additional landslides. Early Wednesday morning there was apparently a rockslide between Tverrdalen and Sverdrupbyen.

Mild weather and more rain are forecast during the coming days.

"We need to have continual conversations with professionals, and as such the question is whether the weather will hit and if there is more going on," Ingerø said.

She said it was important that the governor's office asked city officials to participate in the helicopter survey.

"We saw that many streams disappeared into the ground and that undermined that it was plugging up the river, which could result in a flood wave in the river bed," she said. "That should be an assessment with regard to those going out and working as well."

Nøkkelord

Se bildet større

Alexander Prokop scans the landslide area at the cemetery Tuesday with a laser. The thickest layers after the landslide were up to five meters thick. FOTO: Holt Hancock

Se bildet større

The yellow markings on the map shows the landslides. FOTO: Unis/Norsk Polarinstitutt

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