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Permafrost: Massive Ice

See also | General Facts | Climate Change | Cryostructures | Patterned Ground |  

Massive ice describes ice features that are large in extend and consists mostly of ice. These include ice wedges, thermokarst-cave ice, large segregated ice, buried ice and pingo ice. Segregated ice can obtain dimensions large enough to be considered a massive ice body. The tunnel has wonderful exposures of ice wedges, large segregated ice, and thermokarst-cave ice. The other types of massive ice, that is not seen within the Tunnel, includes buried ice and pingo ice. Buried ice is surface ice that was covered by sediments before it thawed, such as glacier ice and snowbanks. Pingo ice is found at the center of pingos, which form within permafrost regions.

  Ice Wedges Return to Top  

Ice wedge formation is depicted in the figure below. The process begins during the winter where the cold air and ground temperatures cause the ground to contract and then crack in a polygonal pattern, similar to cracked mud flats but at a much larger scale. One observer explains his first strange experiences with the frost cracks below: "During the Arctic winter, frequent reports are heard, coming apparently from the ground. Often the sound is accompanied by a distinct shock, which is in fact an earthquake of sufficient intensity to rattle dishes, etc."

During the following spring and summer, these millimeters wide cracks will fill with melt water mixed small amounts of soil and air that freezes within the permafrost. This process will continue almost every year for centuries or millenniums, which leads to hundreds or thousands of vertical ice layers. The depth of the cracks varies each year causing more ice layers at the top than at the bottom of the ice wedge, which makes the ice wedge grow laterally larger at the top and into a wedge shape. The vertical ice layers that contain small amounts of suspended soil and air bubbles will cause the overall ice to look foliated, as seen in the photo. Therefore, the ice within ice wedges is termed foliated ice.

Within the tunnel, the ice wedges are no longer actively growing. These ice wedges are syngenetic ice wedges and are truncated in many places, with an occasional new ice wedge growing right out of the top of the truncated ice wedge. There is also evidence of two distinct sets of ice wedges, with the first and lower set ranging in age of about 25,000 to 33,000 years. The second and upper set ranges in age of 10,000 to 14,000 years. In between the two sets is thought to be a climate change event. One of the ice wedges is dated from viable living bacteria that was collected and dated to be 25,000 years old.

Diagram of the ice wedge formation. Man pointing to an ice wedge in the tunnel's Winze section.
Diagram of ice wedge formation. Ice wedge in the tunnel's Winze section.

  Thermokarst-Cave Ice Return to Top  

Thermokarst-cave ice is formed through thermal erosion, where surface water vertically migrates downward into the ground and along the ice wedge. Then the surface water can flow laterally along the ice wedge, eroding underground conduits for water flow. The conduit of water can eventually refreeze and form thermokarst-cave ice. The ice is similar to lake and river ice with occurrence of columnar ice, however these columns point inward toward the center of the conduit, instead of downward like lake and river ice, due to the freezing front coming from all sides. Commonly surrounding the thermokarst-cave ice is reticulate-chaotic cryostructure, where saturated sediments that are often emplaced by the intruded water refreeze in a unique pattern. Interestingly, ice veins will cross-cut some of the thermokarst-cave ice and reticulate-chaotic cryostructure as the ice wedges continue to grow after the thermal erosion event. These superposition features that are found in the tunnel demonstrate that these ice bodies were intrusive to the already existing ice wedges.

The two photos show thermokarst-cave ice that has cross-cut an ice wedge. The first photo shows a small ice wedge that was truncated by thermokarst-cave ice. The ice wedge is the lower ice feature that is brown with whitish foliations and the thermokarst-cave ice is the whitish upper ice feature with iron staining, where the iron staining comes from dissolved minerals within the intrusive surface water. The silt seen in between the ice features is reticulate-chaotic cryostructure, where much of the ice at the surface has sublimated away and left a jagged appearance. The second photo shows larger ice features, where an ice wedge is visible at the thigh height of the tour guide and again at his head height. The thermokarst-cave ice is at chest height and includes whitish ice and the iron colored ice. The reticulate-chaotic cryostructure is seen below the thermokarst-cave ice, where a series of research bore holes are running through it, and at the top of the photo where there is a second thermal erosion event.

Man pointing to thermokarst-cave ice. Wedge and cave.
Thermokarst-cave ice. Wedge and cave.

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