New insights into ice ridge keels

New insights into ice ridge keels

Top image: Parts of Aleksey Shestov’s fieldwork was done in the Fram Strait. Photo: UNIS.

Ice ridge keels can potential damage the subsea installations in the Arctic. PhD candidate Aleksey Shestov has investigated the thermodynamic consolidation of ice ridge keels and developed a mathematical model for ice ridge dynamics. Shestov will defend his PhD thesis on Thursday 3 October at UNIS.

1 October 2013
Press release from UNIS and NTNU

Many engineering challenges are currently posed by the Arctic and the sea ice found there. Ice ridge keels have attracted significant attention because of the potential damage they can inflict on subsea installations. Ice Ridges are result of ice cover compression caused by combination of current, wind and thermal expansion forces. Such compression leads to the breaking of the ice cover at the contact line between drifting ice fields. Ice blocks, which are formed during breaking, are subjected to further extrusion on top of the level ice and into the water under ice. The ridge keel is the part of the ridge that is below the water surface.

The formation of seabed gouges in the winter has been documented and it has been hypothesised that moving ice ridge keels can gouge seabeds. Pipelines, power and communication cables and other subsea structures can also be affected by ridge keels.

Measuring sea ice

Aleksey Shestov performing measurements in the sea ice ridge keels. Photo: UNIS

In the industry, the aforementioned structures are typically protected from the effects of ridge keels by burial into the seabed soil. This method is enormously expensive for linear structures such as pipelines and cables. The deeper the burial into the soil, the higher is the cost. Thus, the salient issue in industry is to strike a balance between safety and profit.

This issue is obviously very complicated and has been the subject of interdisciplinary research by the international community, which has resulted in the formulation of international standards.

Aleksey Shestov focused on the physical and mechanical properties of ridge keels and the processes which can provide sufficient strength for keels to interact with the seabed and potential structures.

Keels can be considerably strengthened through consolidation. Atmospheric cooling during the winter season causes a consolidated layer to form in the keel.

In the thesis he concluded that there are different physical processes for the thermodynamic consolidation of keels in the spring and summer seasons and the thermodynamic consolidation of ice ridge keels in water at varying freezing points is a significant research topic in his thesis.

A mathematical model was developed for the ice ridge dynamics associated with the seabed gouging process and the ice-seabed interaction. The model was used to create a geographic information systems module to predict the trajectory and depth of the gouge in monitoring Baydaratskaya Bay. In addition, he determined the physical properties of old ice ridges in the Fram Strait and the dynamic characteristics of fast ice in the Van Mijenfjorden.

Also a physical mechanism was developed for the thermodynamic consolidation of the ice ridge keels below the consolidated layer formed by atmospheric cooling; this mechanism was studied by laboratory experiments, analytically, and numerically.

Aleksey Shestov

Aleksey Shestov. Photo: Eva Therese Jenssen /UNIS

Dissertation
Aleksey Shestov will defend his PhD thesis “The Role of the Thermodynamic Consolidation of Ice Ridge Keels in the Seabed Gouging Process” on Thursday 3 October at 13:15 in auditorium Lassegrotta at UNIS.

Shestov will give a public trial lecture, entitled: “The Physics of the Formation of Ice Ridges in Drift Ice Fields” at 10:15 on Thursday 3 October in Lassegrotta.

About the candidate:
Aleksey Shestov (born 1985) is from Ryazan, Russia. He completed his MSC degree in 2008 at the Moscow Institute of Physics and Technology. In October 2008 he started his PhD work at NTNU and UNIS.

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