Forty-four AC electrical resistivity soundings have been made on the Manitounuk Islands (55°30′N, east coast of Hudson Bay) as well as in post-glacial and Recent marine sediments of the supratidal zone along the east shore of Manitounuk Strait. The results indicate that permafrost, which may have a thickness of 30 m, is present within basalts and quartzites of the cuestas at elevations above 20 m. The thermal effect of the sea and the possible infiltration of sea water in the structural elements prevent the formation of permafrost at lower altitudes. Rocky sites where permafrost has been detected are windswept areas devoid of snow. Heaved bedrock landforms are numerous on those sites. Along the east coast of Manitounuk Strait permafrost is scattered in patches and the permafrost landforms are degrading. Seasonal freeze–thaw processes are responsible for many features, such as thufurs, boulder heaving, clastic dykes, mud volcanoes, and others. The processes are related to year to year variability in the temperature regime, snow depth over the land surface, groundwater movement, thermal effects of the tides, and shore ice on the tidal flat.