[SOUND] [MUSIC] [SOUND] What is a cirque? Is it A, circles in polar deserts formed by stones of different sizes? B, moraines at the end of glaciers that are curved? Or is it C, depressions in mountain sides where snow accumulates to form glaciers. The answer is C. Depressions in mountain sides where snow accumulates to form glaciers. >> In the last episode, we learned about the landscapes of the Arctic and the landforming processes. And we saw that permafrost was one of the features that controls the land. And just as an introduction to this episode, here you see one of many many examples of how permafrost creates a very, very spectacular landscape in the Arctic. This is pasting ground ice wedged polygons. Permafrost, what is it? Well permafrost is ground that remains frozen for two or more years. It is beneath about 20-25% of all the land masses in the Northern Hemisphere. So it's very important. It occurs from the north of the Arctic, where it's continuous. Wherever you dig in the ground, you'll come across permafrost basically. All the way to the southern limits of permafrost where it gradually breaks up from being continuous it becomes discontinuous, sporadic, and then isolated. The thickest permafrost in the world is about one half kilometers thick. It is very substantial. And the oldest permafrost is about three million years old. It's also found on the continental shelves, and you can see this green hatching here off the coast of Siberia. There's permafrost there, too, but that's outside the scope of this series even though it's extremely important permafrost. But I want to reassure you, that permafrost is not a substance, not soil or bedrock, it's everything that remains frozen for more than two years. As I mentioned, it creates many, many features. All the way from the mountains, where you can see rock falls, active land detachment where the soil just slides off, the permafrost to thaw lakes, where the permafrost is thawed or a depression has opened up, and water accumulates. And then the polygonal tundra, the ice wedge polygonal tundra that you saw in the first opening slide. So it has a very big impact on the way the environment looks. And just to reconfirm that, here. Are some rock cracks where there's been permafrost in rocks, and that has opened up movements and dynamics in the rock face. You see Pingos. These are hills, quite large hills, that are created by ice coming together, aggregating in the permafrost area, and pushing the ground up. Other examples you've already seen the ice wedge polygons. Here you see a dynamic where some of the polygon centers are sinking, getting wet, and creating ponds. On the right you see what happens when some of that permafrost, some of the ice wedges thaw. And you see a bridge of the active layer over where there was ice, where there was permafrost. Other examples, palsas. Palsas are peat mounds, individual mounds with permafrost inside a frozen core, and when they start to thaw out and break up as it gets warmer, they create these small thaw lakes. In other examples of thaw slump, is where the active layer just completely detach from the whole area and slides downhill or into a lake. So let's look now at what happens In the dynamics of permafrost, in a normal situation where we don't have climate change. The animation shows you the surface of the tundra, with shrubs and grasses and mosses and the depressions and lichens on the little hammocks, and below that, we have the active layer. You'll see the active layer is greater than 0 degrees C in late summer, it's thawed it. Below that, it can be soil, it can be bedrock, it can be various materials. But then we have the permafrost, which is less than 0 degrees c, it's frozen. And in that, you see little white shapes. These are ice lenses within that permafrost, and they vary in their size and their distribution. And below that we have the unfrozen bedrock, which goes all the way down. As we go into Autumn, early winter, something different happens in the Arctic than elsewhere. In many places, you'll have what we call two-sided freezing. So it gets cold on the surface as the weather gets colder, and also the permafrost surface, the active layer just above that freezes too. So the active layer is squeezed between these two freezing fronts. And you can see the vegetation starting to change into its autumn colors. As we go into late winter, then, of course, we have snow. By this time, all the active layer is frozen, and below that, of course, we have the permafrost and then the unfrozen bedrock. I would also say that as the whole of the active layer freezes, that also produces some features, that are important in ecology. There is a displacement of the surface, there is upward heave, we call it frost heave. And as we have that frost have, we can have cracks in the surface developing. And very often, young seedlings of plants are literally thrown out of the ground because of this freeze thaw process. And this is one of the limitations to agriculture in the north. When we go into the next early Summer, then we come to the thaw period. And now, the shrubs are producing their buds, the snow is disappearing, the surface is wet. And the top of the active layer is thawed out. But still the base of the active layer is thawing and the is going down. But it will stop at the permafrost table. If we now look at the situation in a warming climate, then what we see, and we see increased grass growth and increased shrub growth. We see at the surface of the permafrost where the permafrost meets the active layer that some of the ice lenses have actually thawed, and there you see wet soil. But that has led to a little bit of subsidence, so you now see the topography of the surface changing a little bit more with the depressions being slightly bigger depressions and the humits being slightly higher humits. And eventually we go to a situation where those depressions get very big or much bigger and water accumulates and we have now a thermokarst pond or a thaw pond. And also the vegetation is changing because now we have open water so we have sedges like the cotton grass. The shrubs are growing because of warmer climates. And look at the permafrost. The permafrost now, is not everywhere, it's isolated into a small patch. And that patch is very, very thin. And the permafrost is basically been reduced while the active layer has grown. If we want to know what is happening to our permafrost now, then there are two ways of doing that, basically. One is to take a drilling rig into the arctic, which is not trivial, to drill a bore hole, and to measure temperature in that bore hole for tens of years. Another way, as in the other photo, is to get an implement that you can press through the active layer, until you hit the permafrost level. And then, by measuring how the active layer grows. In thickness, that tells you about how the permafrost is receiving down the profile. And the graphic at the bottom just simply shows temperatures measure in boreholes around the Arctic from very cold permafrost at minus 16 to some very warm permafrost. And what you can see is that most of our permafrost is warming. And in some areas the permafrost is disappearing. What happens when the permafrost disappears? Well if that permafrost area is rich in ice then you have subsidence. When you have subsidence there are major impacts for infrastructures. Houses fall down, roads break up, air strips break up, oil pipelines break. If they're not properly engineered. To properly engineer them, as in this case from a Russian settlement on. There the houses have been insulated from the ground below. So the heat from the houses does not affect the permafrost, but all this has economic cost associated with it. In the natural system, the subsidence leads to trees falling over. This is called the drunken forest, because the subsidence leads to trees just falling over. The permafrost also affects hydrology. That's the way the water flows. And you saw that example from the animation of how a pond is created. Here is a another example. What you see in the middle, this dry tract going up is the edge of some pulsar but a pulsar is degraded as a permafrost is thawing and creating that wet area to the right and to the left. You see the white flowers the cotton grass, you saw those in the animation too. The thawing permafrost also affects land atmosphere links, and I already mentioned in the very first introduction to the course about how permafrost protects carbon that was captured thousands of years ago. And when the permafrost thaws, that carbon is released to act as a greenhouse gas or a pollutant of ice, altering the out beat of ice and snow. And here is one example which is, to my knowledge, is a most extreme example which is from the New Siberian Islands where the rate of coastal erosion's about 40 meters a year. And here you see carbon blowing off when it's dry weather onto the sea ice, you see carbon going, as a gas into the atmosphere, and you also see that in the rain, it's going down into streams and flowing out to the Arctic ocean. At least three different major ways that carbon is being lost from the safety of being stored in permafrost. Permafrost, to some extent, is protected by peat in the sub-arctic lowlands. Because the peat insulates it from warm summer temperatures. But permafrost is also insulated by snow against the winter temperatures. So as the snow cover increases, so the permafrost thaw rate increases, too. And here, you see a very simple experiment, with snow fences that trap snow on one side and deplete snow on the other side. Where you have the accumulation of snow, the permafrost falls faster there than where there is less snow. >> Is permafrost A. Permanently frozen water. B. Permanently frozen soil. C. Permanently frozen sediment. D. Permanently frozen rock. E. All of the above. or F. None of the above.
