The great glaciers of the past carved these fjords, or drowned valleys, out of the mountains like great troughs. Landslides help widen the troughs as the glaciers remove the bedrock support on upper slopes. Huge icebergs may last a week or more. Colors betray a berg's nature or origin. White bergs hold many trapped air bubbles.
Blue bergs are dense.
Greenish-black bergs calved off of glacier bottoms. Dark- striped brown bergs carry morainal rubble from the joining of tributory glaciers, or other sources. Bergs may be weighed down, submerged even, by rock and rubble. A modest- looking berg may suddenly loom enormous, and endanger small craft, when it rolls over. The world of science came to Glacier Bay to observe the great glaciers and found here the ideal natural laboratory for the study of the infant theory of plant succession.