Artisan wells in mid and low latitudes
When you were in seventh grade or so, you probably learned about artesian aquifers and wells. In our my, the example was the Parisian basin. The largest and deepest artesian basin in the world is the Great Artesian Basin in Australia that provides reliably fresh water in wide areas of inland Australia.
Artesian aquifers are confined between two impermeable layers. These layers can be made of rocks, and clay, and in high latitudes or at high altitude permafrost. These impermeable layers cause the aquifer in between to be under positive pressure. The groundwater is refilled where the water carrying layer is exposed to permeable soil at a higher altitude than the location of the well. Here rainwater or water from melting snow can percolate thru the soil and enter the aquifer. Since the location is at a higher level than most of the aquifer, pressure builds up in the aquifer.
When a well is drilled at a location close to the bottom of the basin or at heights below the height of water entrance, the ground water pours out against the gravity force all by itself. Think of this process like opening a bottle of club soda. The bottle is under pressure and uncontrolled opening leads to a fountain.
Artesian wells exist also in Alaska
When I came to Alaska, I heard about artesian wells confined by permafrost in the tundra. One of them is on a southern tundra covered slope of the Brooks Range in the Chandalar River valley about 275 miles (443 km) north of Fairbanks. It spits out an about knee-high, 10 to 12 inch wide fountain of ice cold water in the tundra. Bush pilots report that they have seen artesian wells also in a few other valleys north of the Arctic Circle.
Permafrost can create artesian wells
In contrast to the the artesians well of the Parisian and Great Artesian Basins, in the tundra, artisan wells are created by thick permafrost layers that pressurize the groundwater. At the location of the artesian well, the high-pressure groundwater finds its way thru the permafrost.
Permafrost coins the landscape
The term permafrost refers to soil that stays frozen for at least for two consecutive years. Actually, most permafrost is often frozen for several thousands of years. Above the permafrost, a layer exist that thaws annually in summer. This layer called the active layer permits vegetation to grow in summer. Since the ground below stays frozen over summer, roots cannot take up water from layers deeper than the thawed active layer. Consequently, the flatter the active layer is, the lower vegetation is that it can support. Thus, you can recognize permafrost by the vegetation.
The water cannot penetrate thru the permafrost. Since evapotranspiration (scientific term for the sum of transpiration by vegetation and evaporation of water from the soil surface) is low in the tundra during Alaska’s summers despite the long white nights, the tundra is sort of muddy. Thus, at higher altitudes than the well, in areas of discontinuous permafrost, water can enter the aquifer between permafrost or other impermeable layers.
Frost blisters and pingos can create fountains
Another mechanism that may create fountains in Alaska’s permafrost underlain tundra landscape are so-called pingos and frost blisters. Frost blister are created when the freezing of the active layer in early winter blocks groundwater upward flow from beneath by permafrost. Once this seal pops, pressurized groundwater spits out as a fountain.
The term pingo refers to soil-covered ice that can be as high as 230 ft (70 m). Pingos are “leftovers” of the glacier ice edges of the last ice age. The annual cycle of freezing and thawing creates runoff that refreezes in ice wedges in fall. Water trapped between ice layers may get pressurized and exit as a fountain when it breaks thru the frozen layer.
What I’m wearing
I wore the outfit shown in this post at work on Casual Friday. After work, we had dinner at the Pumphouse, an old Alaskan historic place. They have some old mining equipment on the lawn that make a nice background for outfit photos. In old times in summer, the pump house served to pump water from the Chena River. The water was used to wash gold out of the dirt that miners dug out of the discontinuous permafrost during the cold season.
Did you know that there are artesian wells in Alaska?
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Photos: G. Kramm
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