In this video adapted from KTOO, explore the historic cycle of advance and retreat of tidewater glaciers in southeast Alaska. Over the past 250 years, most glaciers in this region have lost more of their mass through melting and calving than they have gained through the new accumulation of snow and ice. This signals the end of a cooling trend called the Little Ice Age, which lasted nearly 3,000 years. If this period of retreat is extended by global warming, scientists warn that it may result in outright loss of the glaciers.
Ice and climate are inextricably linked. Both the volume of ice and the rate of glacial movement around the world change as Earth's surface temperatures warm and cool—by even the smallest measure. When ice reflects sunlight, it prevents additional heat from being absorbed by water or land, so the ice-free surface changes from light to dark, absorbing more heat. This results in even greater warming on a global scale.
Tidewater glaciers are glaciers that flow from land into the sea. Beginning at the land-sea boundary, the glacier's massive base forges a deep channel as far as the glacier advances. The ice surface is typically jagged, and numerous small icebergs calve off at its leading edge, or margin. Here, a glacier's vertical face may extend 200–300 feet above the water line, its base as deep as 1,000 feet underwater. As with any glacier, climate factors such as temperature and precipitation influence whether tidewater glaciers advance or retreat. As a tidewater glacier begins to recede, its margin moves back through the deepwater channel and becomes less stable. This causes it to calve even more ice. As a result, the annual rate of glacial retreat (100–2000 meters/year) can be much greater than its advance phase (20-40 meters/year).
The tidewater glaciers in Alaska's Inside Passage, the name for the area that encompasses the ocean and islands in the state's southeast "panhandle," formed during a 3,000-year cooling period known as the Little Ice Age. These glaciers are now shrinking. While warming and cooling in the Arctic are part of a natural cycle of climate variability that has been documented by studying ice cores from Greenland, the scientific community agrees that human use of fossil fuels, which began more than 200 years ago, has accelerated glacial melting. This melting threatens the existence of many tidewater glaciers.
From today's research into Alaska's tidewater glaciers, glaciologists are learning more about their historical movements to gain valuable insights into past climate conditions. As ice calves off a glacier and recedes into the mountains, it gradually exposes areas of land covered with trees that were run over by the glacier during its advance. Dating the trees through the study of their growth rings—a process known as dendrochronology—allows scientists to know more about the timing of past advances and retreats. Analyzing core samples from glaciers can also yield information about the glacier's history. These data may in turn help them understand the past climate history of the region, and determine the degree to which human activity is responsible for the most recently observed warming trend.
Academic standards correlations on Teachers' Domain use the Achievement Standards Network (ASN) database of state and national standards, provided to NSDL projects courtesy of JES & Co.
We assign reference terms to each statement within a standards document and to each media resource, and correlations are based upon matches of these terms for a given grade band. If a particular standards document of interest to you is not displayed yet, it most likely has not yet been processed by ASN or by Teachers' Domain. We will be adding social studies and arts correlations over the coming year, and also will be increasing the specificity of alignment.