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Three first-year ice ridges have been examined with respect to geometry and morphology in landfast ice of Shokal'skogo Strait (Severnaya Zemlya Archipelago) in May 2018. Two of the studied ice ridges were located on the edge of the ridged field and were part of it, because their keels extended for a long distance deep into this field. Ice ridges characteristics are discussed in the paper. These studies were conducted using hot water thermal drilling with computer recording of the penetration rate. Boreholes were drilled along the cross-section of the ridge crest at 0.25 m intervals. Cross-sectional profiles of ice ridges are illustrated. The maximal sail height varied from 2.9 up to 3.2 m, the maximal keel depth varied from 8.5 up to 9.6 m. The average keel depth to sail height ratio varied from 2.8 to 3.3, and the thickness of the consolidated layer was 2.5-3.5 m. The porosity of the non-consolidated part of the keel was about 23-27%. The distributions of porosity versus depth for all ice ridges are presented.

Some features of external and internal structures of one-year hummocks formed as a result of multiple interaction of ice fields in various time intervals are considered. Using the concrete results of field researches of ice hummocks as examples, both the main differences in their structure as compared with the single hummocks and common features arisen under certain hydrometeorological and ice conditions are demonstrated.From the point of view of the structure and, especially, of formation mechanisms, the ice hummocks formed as a result of multiple interaction of ice fields are one of the most complex types of ice formations. Unlike the hummocks formed due to the single hummocking of ice floes, these ice formations have a number of typical features in its external and internal structures. The most pronounced of them is the deepening of the consolidated part of originally formed hummock to a quite significant depth [1]. It is observed when the interaction of the primary hummock with the ice fields occurs in rather significant time intervals. As the results of field researches carried out in the southeastern part of the Barents Sea using the thermal drilling method demonstrate [3], the consolidated part of the block hummock with the thickness of more than 3 m may be sunk to the depth of 6-9 m at the repeated hummock formation (Fig. 1).One of the signs of secondary hummocks is the formation of two or several ridges of their above-water part situated most frequently at different angles to each other ( Fig. 2) with ice field pieces of different thickness. However, as the field researches showed [1], when two hummock ridges are situated parallel to each other or mutually perpendicularly, such complex ice formation could be also formed as a result of the single interaction of ice fields. At the usual location of hummock ridges, one of them (the side one) is shorter than another one (main), as a rule, because it is formed at the final stage of hummock formation due to the inhomogeneous distribution of compression load along the main ridge. If the deepening of consolidated part at any segment of the initial ridge does not occur during the formation of secondary hummock ridge, a significant difference in the thickness of their consolidated layers can be observed at further freezing of ice pieces in both ridges. The primary ridge can be identified by ice pieces in the surface part of the hummock being more fritted under the influence of solar radiation.One more important characteristic of multiple-formation hummock structure is the shift of the hummock sail relative to its keel. Much less frequently, this phenomenon may be also observed in usual hummocks formed as a result of the single interaction of ice fields and is well represented in the form of mathematical model developed by M.A. Hopkins [2]. According to this model and laboratory researches [1], the main condition of the formation of such hummocks is the interaction of ice fields differing in thickness as 3:1 and more. Usually, such difference is observed near the p...