The Columbia Glacier in Alaska surged during the early part of this century. This photograph from 1909 shows the terminus of the glacier knocking over trees as it advanced. Columbia Glacier is located in the Chugach Mountains of Alaska. —Source: Unattributed photograph at the National Snow and Ice Data Center, University of Colorado, Boulder

Columbia Glacier in Alaska encroached on a forest as it surged in the early twentieth century, pushing trees, soil, rocks and debris as it advanced. This photograph was taken in 1914, several years after the glacier had begun to surge. Columbia Glacier is located in the Chugach Mountains of Alaska. —Source: D. K. Handy photograph at the National Snow and Ice Data Center, University of Colorado, Boulder

A researcher investigates the terminus of Hole-in-the-Wall Glacier as it pushes debris in front of it and knocks over trees. This photograph dates from 1959, when the glacier had already been surging for nearly 20 years. —Source:Unattributed photograph at the National Snow and Ice Data Center, University of Colorado, Boulder

Hole-in-the-Wall Glacier knocking over trees in an advance over terrain not covered since the eighteenth century. Hole-in-the-Wall Glacier is located in the coastal mountains of southeast Alaska and is a tributary of Taku Glacier. —Source: Unattributed photograph at the National Snow and Ice Data Center, University of Colorado, Boulder