Mysterious glacial passage
Less than 12,000 years ago, which geologically speaking was just yesterday, the last great ice age melted to an end. Throughout the history of Earth, there have been several ice ages. During each ice age, glaciers advanced and retreated, leaving a mysterious story of their passage. One such mystery is that of the landscapes of Maine. Research indicates that just 12,000 years ago, Maine as we know it did not exist! Where was Maine during the millions of years prior to the last climate shift? Scientists are uncertain, but, thanks to Maine's intriguing Ice Age Trail, we know that the landscapes lay buried beneath glacial ice during the last great ice age.
Alpine Glacier Photo courtesy of John Gomes/Anchorage Alaska Vast ice sheets, very similar to the ones that now cover the majority of Greenland and Antarctica, covered a significant portion of the North American continent long, long ago. Once concealed beneath the last of these massive ice sheets, the landscape of Maine tells a unique story of a previously unknown world. Come along with us as we journey down Maine's intriguing Ice Age Trail and discover what ancient geological mysteries and marvelous marine life the retreating glacier left behind.
Believe it or not, glaciers exist on every continent, including Africa. However, most of the world's glaciers are found near the poles. There are two main types of glaciers, also known as ice sheets: continental glaciers and alpine (valley) glaciers. Continental glaciers are associated with ice ages and can cover extremely large areas. Continental glaciers are enormous masses of ice that can overwhelm the landscape and extend over an area's entire surface. Currently, Antarctica and Greenland are the only places in which continental glaciers still exist. Alpine glaciers are much smaller and form in mountain terrain, from which they flow down the surrounding valleys. Glaciers require very specific climate conditions and are found mostly in regions of high snowfall in winter and cool temperatures in summer. These conditions ensure that snow that accumulates in the winter is not lost due to melting, evaporation or calving (breaking at an edge or separating) during the summer months. Such conditions typically prevail in polar and high alpine regions.
Continental Glacier Photo courtesy of John Gomes/Anchorage Alaska When glacial ice becomes extremely dense, the color often appears to be blue. Due to years upon years of compression, the ice gradually becomes denser over time, forcing out tiny air pockets between crystals. When glacial ice is extremely dense, the ice absorbs all other colors in the spectrum and reflects primarily blue, which is the color we see. When glacial ice is white, this usually indicates that there are many tiny air bubbles still in the ice.
What is going on with glaciers now?
- Presently, 10 percent of land is covered by glaciers.
- Glaciers store about 75 percent of the world's freshwater.
- During the last great ice age, glaciers covered 32 percent of the total land area of the globe.
- Glacier ice crystals can grow to be as large as baseballs.
- In the United States, glaciers cover over 75,000 square kilometers, with most glaciers located in Alaska.
- Almost 90 percent of an iceberg is below water; and only about 10 percent shows above water.
- The Antarctic ice sheet has been in existence for at least 40 million years.
- In Washington state alone, glaciers provide 470 billion gallons of water each summer.