Sunday, October 20, 2019
Overview of the Last Glaciation
Overview of the Last Glaciation When did the last Ice Age occur? The worlds most recent glacial period began about 110,000 years ago and ended around 12,500 years ago. The maximum extent of this glacial period was the Last Glacial Maximum (LGM) and it occurred around 20,000 years ago. Although the Pleistocene Epoch experienced many cycles of glacials and interglacials (the warmer periods between the colder glacial climates), the last glacial period is the most heavily studied and best-known portion of the worlds current ice age, especially with regard to North America and northern Europe. The Geography of the Last Glacial Period At the time of the LGM (map of glaciation), approximately 10 million square miles (~ 26 million square kilometers) of the earth was covered by ice. During this time, Iceland was completely covered as was much of the area south of it as far as the British Isles. In addition, northern Europe was covered as far south as Germany and Poland. In North America, all of Canada and portions of the United States were covered by ice sheets as far south as the Missouri and Ohio Rivers. The Southern Hemisphere experienced the glaciation with the Patagonian Ice Sheet that covered Chile and much of Argentina and Africa and portions of the Middle East and Southeast Asia experienced significant mountain glaciation. Because the ice sheets and mountain glaciers covered so much of the world, local names have been given to the various glaciations around theÃ world. The Pinedale or Fraser in the North American Rocky Mountains, Greenland, the Devensian in the British Isles, the Weichsel in Northern Europe and Scandinavia, and the Antarctic glaciations are some of the names given to such areas. Wisconsin in North America is one of the more famous and well-studied, as is the WÃ ¼rm glaciation of the European Alps. Glacial Climate and Sea Level The North American and European ice sheets of the last glaciation began forming after a prolonged cold stage with increased precipitation (mostly snow in this case) took place. Once the ice sheets began forming, the cold landscape altered typical weather patterns by creating their own air masses. The new weather patterns that developed reinforced the initial weather that created them, plunging the various areas into a cold glacial period. The warmer portions of the globe also experienced a change in climate due to glaciation in that most of them became cooler but drier. For example, rainforest cover in West Africa was reduced and replaced by tropical grasslands because of a lack of rain. At the same time, most of the worlds deserts expanded as they became drier. The American Southwest, Afghanistan, and Iran are exceptions to this rule however as they became wetter once a shift in their airflow patterns took place. Finally, as the last glacial period progressed leading up to the LGM, sea levels worldwide dropped as water became stored in the ice sheets covering the worldÃ¢â¬â¢s continents. Sea levels went down about 164 feet (50 meters) in 1,000 years. These levels then stayed relatively constant until the ice sheets began to melt toward the end of the glacial period. Flora and Fauna During the last glaciation, shifts in climate altered the worldÃ¢â¬â¢s vegetation patterns from what they had been prior to the formation of the ice sheets. However, the types of vegetation present during the glaciation are similar to those found today. Many such trees, mosses, flowering plants, insects, birds, shelled mollusks, and mammals are examples. Some mammals also went extinct around the world during this time but it is clear that they did live during the last glacial period. Mammoths, mastodons, long-horned bison, saber-toothed cats, and giant ground sloths are among these. Human history also began in the Pleistocene and we were heavily impacted by the last glaciation. Most importantly, the drop in sea level aided in our movement from Asia into North America as the landmass connecting the two areas in Alaskas Bering Strait (Beringia) surfaced to act as a bridge between the areas. Todays Remnants of the Last Glaciation Though the last glaciation ended about 12,500 years ago, remnants of this climatic episode are common around the world today. For example, increased precipitation in North Americas Great Basin area created enormous lakes (map of lakes) in a normally dry area. Lake Bonneville was one and once covered most of what is today Utah.Ã¢â¬â¹ TheÃ Great Salt Lake is todays largest remaining portion of Lake Bonneville but the old shorelines of the lake can be seen on the mountains around Salt Lake City. Various landforms also exist around the world because of the enormous power of moving glaciers and ice sheets. In Canadas Manitoba for instance, numerous small lakes dot the landscape. These were formed as the moving ice sheet gouged out the land beneath it. Over time, the depressions formed filled with water creating kettle lakes. Finally, there are many glaciers still present around the world today and they are some of the most famous remnants of the last glaciation. Most ice today is located in Antarctica and Greenland but some ice is also found in Canada, Alaska, California, Asia, and New Zealand. Most impressively though are the glaciers still found in the equatorial regions like South Americas Andes Mountains and Mount Kilimanjaro in Africa. Most of the worlds glaciers are famous today however for their significant retreats in recent years. Such a retreat represents a new shift in the earthÃ¢â¬â¢s climate- something that has happened time and time again over the earths 4.6 billion year history and will no doubt continue to do in the future.