Contents

06 April 1990
Vol 248, Issue 4951

About The Cover

The mouth of a borehole drilled to the bottom of ice stream B, West Antarctic Ice Sheet. By means of such boreholes, about 1050 meters deep, observations of physical conditions at the base of the rapidly moving ice stream have been made (see page 57). Frost crystals have formed around the hole during overwintering. The mouth of the hole at the snow surface is defined by a circle 12.5 centimeters in diameter cut in plywood. [Photo by B. Kamb]