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Author Topic: Graying/Browning of Snowcover Svalbard  (Read 685 times)

Niall Dollard

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Graying/Browning of Snowcover Svalbard
« on: April 28, 2020, 02:09:00 AM »
Not too sure what to make of this ?

It has been mentioned in other threads that there is a lot of graying in northern Greenland.

Looking at today's Worldview image of Svalbard, shows patches of graying also.

There are some strange looking patches stretching out over the northern part of the wide fjord (Storfjorden) to the east of Sptizbergen.

I then had a closer look back on Sentinel. On 23rd April it shows some brown patches over the southern foothills on the edge of the bay but nothing over the frozen fjord sea ice.

But next image on 26th April  the brown/gray discoloration extends right out over the sea ice.

I accept that the brown on the foothills is where the snow has been removed but what about the part stretching out over the sea ice ?

I wonder is this some sort of processing artefact (shadows) or is it actual soot or something blown out over the ice ?

The Gif attached shows the progression of the "shadows" from 23rd to 26th (oriented 90 degrees)
« Last Edit: April 28, 2020, 02:16:13 AM by Niall Dollard »

Niall Dollard

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Re: Graying/Browning of Snowcover Svalbard
« Reply #1 on: April 28, 2020, 02:14:36 AM »
I forgot to include this sentinel image 260420 showing the land coastline (arrowed).

Freegrass

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IceConcerned

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Re: Graying/Browning of Snowcover Svalbard
« Reply #3 on: April 28, 2020, 07:19:50 AM »
The extension to ice is likely linked to strong winds : look at the clouds and floating ice, they tend to form shapes parallel to the brown extension
As for the original cause, it is difficult to say but rocks or sand and dust being blown off is a possibility. So avalanche, or maybe just aerial erosion?

P-maker

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Re: Graying/Browning of Snowcover Svalbard
« Reply #4 on: April 28, 2020, 07:40:08 AM »
These dark, brown streaks looks like fresh aeolian deposits on the ice. Most likely, a strong blustery wind - with some foehn effect - came from the north. In most of the south-facing valleys on Svalbard, you can see these dark features extending even on to the remaining sea ice.

The darkest streaks can be found where the wind has picked up fine-grained material from fresh lateral moraines, where shrinking glaciers have left it. The net result will be a lower albedo for the remaining part of the melt season - a positive feedback - adding to the loss from sea ice, which has been blown out of the fjords in many places on this same occasion.

Niall Dollard

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Re: Graying/Browning of Snowcover Svalbard
« Reply #5 on: April 28, 2020, 10:25:39 AM »
Thanks for replies.

I had a look at Svalbard weather data around that time. Nothing of note from Longyearbyen located to the west of the area in question, but the stats from another (nearer) station Edgeoya, located a little to the east, support  P-maker's last comment.

That station did have persistent strong northerlies on the 25th gusting to 86 km/hr. Temperatures were circa -10 C.

So likely blown off dust.

At least restores my faith in the satellite images but all this graying/browning so early in the year is a worry.

P-maker

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Re: Graying/Browning of Snowcover Svalbard
« Reply #6 on: April 28, 2020, 01:46:19 PM »
Niall Dollard:

Quote
... blown off dust.

No, my friend. Even better than that. Thanks to your fine table, I will retract my remark about Foehn effect. Instead, I will suggest strong katabatic winds (15-20 m/s) laden with drifting snow at temperatures below -10 C.  This must have been an inferno with chill factors way below -20 C. Drifting ice particles at those wind speeds and temperatures are highly abrasive. Thus, the resulting mixture of ice and mineral fragments have formed an extensive layer of niveo-aeolian sediment downwind from the steepest slopes, where ice particles have bombarded fresh lateral moraines for about 24 hours.

Similar niveo-aeolian sediments (called cover sands) of Late-glacial age covers wide areas of NL, DE and PL.

Niall Dollard

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Re: Graying/Browning of Snowcover Svalbard
« Reply #7 on: April 28, 2020, 02:12:34 PM »
Thanks again P-Maker for pointing me in the right direction

Sounds like it would have been horrible conditions for any human to be caught out in. The dark patch is approx 3km wide and extends nearly 6km over the sea ice.

Googling brought me to this research paper of a study conducted in the Ebba Valley, Svalbard, just to the NW of the images.

https://www.researchgate.net/publication/299537704_Characteristics_of_aeolian_and_niveo-aeolian_deposits_in_central_Spitsbergen_Ebba_valley

This paper mentions "It is interesting that the biggest amount of aeolian material is not transported from the south-west but from the north (38%), northeast (28%) and northwest (18%), so from the direction where strongest winds were observed. "


P-maker

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Re: Graying/Browning of Snowcover Svalbard
« Reply #8 on: April 28, 2020, 07:36:29 PM »
Niall, you are wellcome.

The same wind directions have actually been inferred from the late-glacial cover sands in Europe.

The thinking goes that the initial layers were caused by lowering of sea level and exposure of wide open sand flats in the North Sea Basin some 20 K years ago. At the same time, permafrost was widespread south of the Scandinavian ice-sheet. Sandfilled ice-wedges in the permafrost were typical.

During the late-glacial period from 15-13 K years ago, the ice-sheet margin was retreating, leaving lateral moraines and sandar open for the fierce NW-ly winds to pick up material to be deposited mainly during winter. Seasonal frost cracks were common.

Debate is still ongoing about how cover sand deposition developed during the Bølling - Younger Dryas - Allerød fluctuations. The main thinking is that most of the material was just reworked older deposits.

Thus, in a deglacial phase, as we are experiencing now, we should see more of this kind of niveo-aeolian activity.