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Glaciology
The glacier closest to Krossbu is Leirbreen, which is an arm of Smørstabbreen. You can't see it from Krossbu but it is the one right in front of Store Smørstabbtind. The glacier you see further up into the valley from Krossbu is Bøverbreen, which is also an arm of Smørstabbreen. Leirbreen has a magnificent glacial portal or "breport" which is the perfect place for the first lunch break on many of the walks east of Krossbu.
A very important rule on the mountain says that you shouldn't take even one step out on the glacier without rope or other equipment. This is because already the edge of the glacier can be treacherous, and one misplaced foot step or a crack in the ice can result in you sliding far in under the ice on the polished rock, without any possibility to get up again. For a layman it is completely impossible to decide which part of the ice is safe and which isn't, and therefor you really only need to remember one thing. Never take even one step out onto the ice without a guide or equipment. But there are lots of snowfields and ice many places. Is everything as dangerous? No, the snowfields are fine to walk on, as long as you take care not to loose your foothold and slide down into ice water or rocks. The important thing is in other words to know what is a snow field and what is a glacier.
In short and a bit simplified you can say that the snowfield is lying still while the glacier is moving, and the movement is what causes crevices. No rule witout an exception of course. There are snowfields that crack and calve out their lower edge and there are glaciers that are completely still. Snowfields crack of their own weight as opposed to glaciers that crack when moving over an uneven surface. Glaciers that are still are detached rests of a bigger glacier. They have been moving before, but as they melt thinner the movement stops.
You can say that a glacier has a balance line. Above the balance line, not all the winter snow melts away during summer. Instead it packs and stays year after year. Below the balance line the winter snow melts away during summer, together with some of the older, underlying ice. Newfallen snow has a density of appr. 0,1 g/cm3. After the wind has packed it, it reaches appr. 0,3 g/cm3. Compression and re-freezing of melted snow increases the density during summer to appr. 0,55 g/cm3. By and by bigger crystals eat up the smaller ones and together with freezing meltwater the density reaches 0,8 g/cm3. Now the ice is all but airtight and can be called glacier ice.
Above the balance line more and more snow is stored and transformed to ice. In that way the pressure on the underlying ice increases. This causes the ice to slide on the bedrock and the interior of the ice to start transforming and moving. The latter comes from the ice getting plastic, i.e. the deformation velocity of the crystals are greater than the force pressing on them. The glacier is on the slide.
As the ice is moving over the bedrock you get crevasses, mainly of two categories. V-crevasses where the bedrock is bulging out and A-crevasses where the bedrock is bulging in. A V-crevasse is widest at the surface and narrows off into the depth. Here you can get stuck or end up in ice water in the bottom if you fall down. An A-crevasse is treacherously narrow at the surface and widens into the depth. Here you can get a free fall all the way to the bedrock.
Crevasses can also come from differences in velocity between different parts of the glacier. In the outer bend of a glacier that turns a corner, you get rim crevasses perpendicular to the direction of movement. In the inner bend the ice gets pressed together and upwards. Where the glacier is pressed into a narrower passage you get transverse crevasses from the velocity increase and where it widens you get longitudinal crevasses. Along the edges you also get rim crevasses from the friction between the ice and the bedrock.
As the ice comes down below the balance line, as said before, it begins to melt faster than the winter snow can build it up. A glacier in perfect balance always gets its refill from above the balance line, by moving in the same tempo as it melts below the balance line. A glacier moving ahead faster than it melts above the balance line is pushing forward, i.e. the glacier's edge is moved further and further down into the valley. A glacier melting faster than it moves forward is retreating. But when we say that a glacier is retreating it is only the position of the edge we are talking about. The ice is still moving downwards, just not fast enough.
There are also interesting things happening on the surface of the glacier. The ice is rarely completely clean. Instead we find everything from air pollution to large rocks. Sand, rubble, dead lemmings and assorted droppings from the animal life gets heated by the sun and melts its way down through the ice, creating cryoconite holes. Larger rocks on the other hand are insulating the ice, making it melt more around the rock than right under it. By and by it ends up on a piedestal until finally it falls down and the process starts anew. In many places the snow is red. This is a green alga called Clamydomonas nivalis that thrive in summer snow. The red colour comes from the same red pigment, astraxantine, that you find in shrimp shell and the meat of trout and salmon.
Where the glacier moves by it drags with it rocks and stone from underneath and it also gets rocks and rubble that has slid down from the valley sides onto the ice in the edge. All these types of transported stone is called moraine. Ground moraine is the rocks and debris frost shattered and scratched along by the ice. Where the glacier has retreated the last years, like up at Leirbreen, you can see fresh ground moraine, with everything from the finest clay to large boulders. As the years pass the plants make their entrance on the virgin soil.
Lateral moraine is the debris that has fallen from the valley sides and travels downwards on the glacier edges. If the glacier rapidly decreases in thickness you can see the lateral moraine as a wall along the valley side. Where two glacier tounges meet, their lateral moraines form a medial moraine as the debris on the edges now ends up in the middle of the merged glacier. Medial moraines can also start in the middle of a glacier and is in that case comprised of material that is ripped loose from a little rocky knoll under the ice and transported up to the surface a bit further down.
Finally we have the terminal moraine. That is the debris pushed forward by the glacier as it moves forward. As it retreats it leaves a distinct wall of rocks and boulders. If the glacier makes small advances between the retreats you get several parallel terminal moraines.
The glacier is creating the landscape we walk in. Scratchmarks in the rock shows the direction in which the ice has dragged its ground moraine. Small knolls can be rounded off on one side, the one that met the ice, and cut off on the leeward side. This comes from a pressure reduction on the far side with frost shattering and the tearing loose of material as a result. "Giant's kettles", holes in the polished rock, are the result of boulders that have rotated in the rushing water under the ice.
The really big erosion forms we see in the mountains are U- and V-shaped valleys. The U-shaped valleys are those formed by ancient glaciers during the ice ages. The V-shaped valleys on the other hand are the effects of of running water that has dug deeper and deeper into the mountain. But we mustn't think that today's glaciers have anything to do with the U-shaped valleys, even though the principle is the same. The glaciers we see today are just newcomers that have taken the same places the inland ice dug out of the mountain during the last ice ages. Just 8000 years ago, as the ice age was replaced by a mediterranean climate in Scandinavia, all the ice was gone before glaciers were once again starting to form up here.
Walk description
The walk up to the glacial portal is a common first leg for several of the walks east of Krossbu. The glacial portal is worth a visit in its own right and there is nothing wrong in taking the same way back again if you have woken up on the lazy side. The walk described here however, takes a small detour on the way back. That way you get to see both lakes and waterfalls close up.
Start from the front of Krossbu and walk down to the parking on the other side of the wooden bridge. On the far side of the parking a trail starts that follows the stream Leira on its left side. The walk is steeper than it looks so it can be a good tip to both lighten up the clothing and take a break once in a while. Take a moment to enjoy "the Three Sisters", the waterfalls up on the other side of the stream.
The moraine:
N 61°34.358
E 08°04.164
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After a couple of kilometers you reach the largest of the terminal moraines Leirbreen has deposited in front of itself. Here the glacier has butted forwards and back for many years and shoved more and more debris into the long wall we see today. Finally it had to surrender to the climate and has retreated far back to the place where we find the glacier's edge today.
The portal:
N 61°34.540
E 08°04.912
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Up here the stream forks out into many small brooks. Keep an eye open for the small cairns marking the way up along the brooks furthest to left. Finally your reach a sort of plateau which is the new land the glacier recently has handed over. During the last decades the glacier has retreated quite rapidly. By looking for the red marks with a year on some of the larger boulders you can see exactly how fast the retreat has been. Then you just choose a comfortable seat and take your first lunch break in the shimmer of the glacier and with Store Smørstabbtind watching over you.
The inlet:
N 61°35.517
E 08°03.420
The outlet:
N 61°35.529
E 08°02.853
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When you are done with the glaciology studies up by the glacial portal you continue the walk towards northwest, over Veslefjell. The next goal is the east end of Øvre Nufstjørna and the most convenient route is by the two small lakes that lie in an angel to each other on the map. Continue around Øvre Nufstjørna from the stream that runs in to it to the outlet in the other end. Then follow this stream down to a small plateau and take the opportunity to cross the stream, over to its left side here, before the stream is too strong.
The waterfall:
N 61°35.435
E 08°02.397
Krossbu:
N 61°34.444
E 08°01.965
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Now you come to the waterfall that throws itself to the valley floor. You get the best view from the little outcrop on the south side of the waterfall. When you continue back to Krossbu there are two routes to choose from. Alternative one is to go straight down to the road. There is a good path here, but it can be difficult to find the starting point of it. It pays off to find it, otherwise you easily end up in the willow brush. Once down you just follow the road back to Krossbu. The other alternative is to go up some elevation metres again and walk diagonally down the valley side. The latter is of course the finest, even if the road can be tempting for someone who is tired. Length of the walk, appr. 9 km.
Route: BREPORTEN
The moraine: N 61°34.358 E 08°04.164 MORAINE
The portal: N 61°34.540 E 08°04.912 PORTAL
The inlet: N 61°35.517 E 08°03.420 NUFSTJORNA
The outlet: N 61°35.529 E 08°02.853 NUFSTJORN2
The waterfall: N 61°35.435 E 08°02.397 NUFSGROVI
Krossbu: N 61°34.444 E 08°01.965 KROSSBU
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The glacier closest to Krossbu is Leirbreen, which is an arm of Smørstabbreen. You can't see it from Krossbu but it is the one right in front of Store Smørstabbtind. The glacier you see further up into the valley from Krossbu is Bøverbreen, which is also an arm of Smørstabbreen. Leirbreen has a magnificent glacial portal or "breport" which is the perfect place for the first lunch break on many of the walks east of Krossbu.
A very important rule on the mountain says that you shouldn't take even one step out on the glacier without rope or other equipment. This is because already the edge of the glacier can be treacherous, and one misplaced foot step or a crack in the ice can result in you sliding far in under the ice on the polished rock, without any possibility to get up again. For a layman it is completely impossible to decide which part of the ice is safe and which isn't, and therefor you really only need to remember one thing. Never take even one step out onto the ice without a guide or equipment. But there are lots of snowfields and ice many places. Is everything as dangerous? No, the snowfields are fine to walk on, as long as you take care not to loose your foothold and slide down into ice water or rocks. The important thing is in other words to know what is a snow field and what is a glacier.
In short and a bit simplified you can say that the snowfield is lying still while the glacier is moving, and the movement is what causes crevices. No rule witout an exception of course. There are snowfields that crack and calve out their lower edge and there are glaciers that are completely still. Snowfields crack of their own weight as opposed to glaciers that crack when moving over an uneven surface. Glaciers that are still are detached rests of a bigger glacier. They have been moving before, but as they melt thinner the movement stops.
You can say that a glacier has a balance line. Above the balance line, not all the winter snow melts away during summer. Instead it packs and stays year after year. Below the balance line the winter snow melts away during summer, together with some of the older, underlying ice. Newfallen snow has a density of appr. 0,1 g/cm3. After the wind has packed it, it reaches appr. 0,3 g/cm3. Compression and re-freezing of melted snow increases the density during summer to appr. 0,55 g/cm3. By and by bigger crystals eat up the smaller ones and together with freezing meltwater the density reaches 0,8 g/cm3. Now the ice is all but airtight and can be called glacier ice.
Above the balance line more and more snow is stored and transformed to ice. In that way the pressure on the underlying ice increases. This causes the ice to slide on the bedrock and the interior of the ice to start transforming and moving. The latter comes from the ice getting plastic, i.e. the deformation velocity of the crystals are greater than the force pressing on them. The glacier is on the slide.
As the ice is moving over the bedrock you get crevasses, mainly of two categories. V-crevasses where the bedrock is bulging out and A-crevasses where the bedrock is bulging in. A V-crevasse is widest at the surface and narrows off into the depth. Here you can get stuck or end up in ice water in the bottom if you fall down. An A-crevasse is treacherously narrow at the surface and widens into the depth. Here you can get a free fall all the way to the bedrock.
Crevasses can also come from differences in velocity between different parts of the glacier. In the outer bend of a glacier that turns a corner, you get rim crevasses perpendicular to the direction of movement. In the inner bend the ice gets pressed together and upwards. Where the glacier is pressed into a narrower passage you get transverse crevasses from the velocity increase and where it widens you get longitudinal crevasses. Along the edges you also get rim crevasses from the friction between the ice and the bedrock.
As the ice comes down below the balance line, as said before, it begins to melt faster than the winter snow can build it up. A glacier in perfect balance always gets its refill from above the balance line, by moving in the same tempo as it melts below the balance line. A glacier moving ahead faster than it melts above the balance line is pushing forward, i.e. the glacier's edge is moved further and further down into the valley. A glacier melting faster than it moves forward is retreating. But when we say that a glacier is retreating it is only the position of the edge we are talking about. The ice is still moving downwards, just not fast enough.
There are also interesting things happening on the surface of the glacier. The ice is rarely completely clean. Instead we find everything from air pollution to large rocks. Sand, rubble, dead lemmings and assorted droppings from the animal life gets heated by the sun and melts its way down through the ice, creating cryoconite holes. Larger rocks on the other hand are insulating the ice, making it melt more around the rock than right under it. By and by it ends up on a piedestal until finally it falls down and the process starts anew. In many places the snow is red. This is a green alga called Clamydomonas nivalis that thrive in summer snow. The red colour comes from the same red pigment, astraxantine, that you find in shrimp shell and the meat of trout and salmon.
Where the glacier moves by it drags with it rocks and stone from underneath and it also gets rocks and rubble that has slid down from the valley sides onto the ice in the edge. All these types of transported stone is called moraine. Ground moraine is the rocks and debris frost shattered and scratched along by the ice. Where the glacier has retreated the last years, like up at Leirbreen, you can see fresh ground moraine, with everything from the finest clay to large boulders. As the years pass the plants make their entrance on the virgin soil.
Lateral moraine is the debris that has fallen from the valley sides and travels downwards on the glacier edges. If the glacier rapidly decreases in thickness you can see the lateral moraine as a wall along the valley side. Where two glacier tounges meet, their lateral moraines form a medial moraine as the debris on the edges now ends up in the middle of the merged glacier. Medial moraines can also start in the middle of a glacier and is in that case comprised of material that is ripped loose from a little rocky knoll under the ice and transported up to the surface a bit further down.
Finally we have the terminal moraine. That is the debris pushed forward by the glacier as it moves forward. As it retreats it leaves a distinct wall of rocks and boulders. If the glacier makes small advances between the retreats you get several parallel terminal moraines.
The glacier is creating the landscape we walk in. Scratchmarks in the rock shows the direction in which the ice has dragged its ground moraine. Small knolls can be rounded off on one side, the one that met the ice, and cut off on the leeward side. This comes from a pressure reduction on the far side with frost shattering and the tearing loose of material as a result. "Giant's kettles", holes in the polished rock, are the result of boulders that have rotated in the rushing water under the ice.
The really big erosion forms we see in the mountains are U- and V-shaped valleys. The U-shaped valleys are those formed by ancient glaciers during the ice ages. The V-shaped valleys on the other hand are the effects of of running water that has dug deeper and deeper into the mountain. But we mustn't think that today's glaciers have anything to do with the U-shaped valleys, even though the principle is the same. The glaciers we see today are just newcomers that have taken the same places the inland ice dug out of the mountain during the last ice ages. Just 8000 years ago, as the ice age was replaced by a mediterranean climate in Scandinavia, all the ice was gone before glaciers were once again starting to form up here.
Walk description
Start from the front of Krossbu and walk down to the parking on the other side of the wooden bridge. On the far side of the parking a trail starts that follows the stream Leira on its left side. The walk is steeper than it looks so it can be a good tip to both lighten up the clothing and take a break once in a while. Take a moment to enjoy "the Three Sisters", the waterfalls up on the other side of the stream.
After a couple of kilometers you reach the largest of the terminal moraines Leirbreen has deposited in front of itself. Here the glacier has butted forwards and back for many years and shoved more and more debris into the long wall we see today. Finally it had to surrender to the climate and has retreated far back to the place where we find the glacier's edge today.
When you are done with the glaciology studies up by the glacial portal you continue the walk towards northwest, over Veslefjell. The next goal is the east end of Øvre Nufstjørna and the most convenient route is by the two small lakes that lie in an angel to each other on the map. Continue around Øvre Nufstjørna from the stream that runs in to it to the outlet in the other end. Then follow this stream down to a small plateau and take the opportunity to cross the stream, over to its left side here, before the stream is too strong.
