Lake Hoare is one of several perpetually ice-covered lakes in the Dry Valleys of Antarctica. It is located approximately 100 miles west of McMurdo Station, the main US base in the Antarctic.
Lake Hoare's ice cover is approximately 10 foot thick in the center, and thinner at the edges. The outer 100 feet melts during the warmest part of the summer and forms a "moat". The lake continually freezes on the bottom of this ice layer, and during the summer months evaporation from meltwater pools and sublimation remove ice from the top of this ice layer. As a result, the ice is constantly moving slowly upwards. Wind-blown sand collects on the surface of the ice, and because it is darker collects more heat during the summer, causing those areas to melt faster. The rising ice in between the sandy areas forms 1 to 1.5 foot tall "sculptures" that make surface travel difficult on the lake.
Walking on them is not too difficult, all though huge areas can be undercut by melt water and collapse, possibly twisting an ankle. There is no real danger from this (there is still 10 feet of ice underneath the collapsed section), but moving 500 pound drums of diesel over this sort of terrain is rather difficult. Luckily, in years past there have been large meltwater "ponds" that have formed due to the sand, and when these refreeze they leave large flat areas. By finding the best paths through these, large loads can be moved efficiently using sleds, with crampons on the feet for traction.
Also, the moats around the lake are smooth, necessitating crampons for travel, but lacking ankle twisting potential. Of course, as the summer progresses, the moats start to melt, and the teams engaged in research in the Dry Valleys have to use row boats to get to the still solid ice in the center of the lake.