Geoscenario Resources—Glaciers: Geologist Task Now that you have explored as a team the general story of how glaciers shaped the midwestern and northeastern United States, it is time for each of you to dive into more specialized information. The geologist focuses on regional features shaped by glaciers and how they formed. Add helpful details to your notes for Geoscenario Team Questions. Then work together and combine all the information to successfully present your story of glaciers. Questions for the Geologist to Consider • What geological features in this region were formed by glaciers? • What is the geological story of how the features were formed? Information Over a period of 10,000 years (100,000–110,000 years ago), the temperature dropped about 17°C, and the most recent glacial period began (evidence from oxygen ratios and foraminifera data). Around 20,000–35,000 years ago, the Laurentide (or Wisconsin) Ice Sheet covered most of Canada and a large portion of the northern United States. The massive ice sheet scraped away layers of earth materials as it pushed southward. Geologists look for clues today that help them determine the path and rate of glacial movement. The Great Lakes A glacier pushing poorly sorted glacial till in front of it. The glacial till forms a fill basins that the glaciers carved. In other areas, moraine. © iStockphoto/cotesebastien exposed rock displays scrape marks created by advancing ice carrying rocks and debris, called glacial till. Piles of glacial till form landmarks like moraines. Even huge boulders can be carried by glaciers. When geologists spot a boulder in an unexpected place, called an erratic, they often suspect a glacier carried it there. Glacial till being carried along by a glacier as it moves down the valley. As the glacier melts (near bottom of the picture), it deposits till that forms moraines along the sides and in the middle of the glacier. © Bruce Molnia, Terra Photographics A glacier moved over this bedrock. Rocks embedded in the glacier dug these grooves, or striations, in the bedrock. The grooves show which way the glacier was moving. Courtesy of US Geological Society FOSS Next Generation Glaciers—Page 1 of 8 © The Regents of the University of California Version date November 20, 2018 Can be duplicated for classroom or workshop use. 14,000 Years Ago 9,000 Years Ago ICE ICE Lake Chicago Lake St. Lawrence St. Lawrence Algonquin River River Early Lake Ontario Lake Maumee Early Lake Erie These maps show the retreat of the Laurentide Ice Sheet. The meltwater level in the Great Lake basins 14,000 years ago was much higher than it is today. Courtesy National Oceanic Atmospheric Administration. Here are some things to think about that should be part of your story of this region. • Look at the images above. Why didn’t the meltwater flow out the St. Lawrence River 14,000 years ago, as it does today? • Look at the rock column to the right. What happened to the rock in the Great Lakes basin that was less than 400 million years old? Events 25,000–20,000 years ago: Glaciers advancing from the Laurentide Ice Sheet carve out the Great Lake basins. 21,000–18,000 years ago: Terminal moraines deposit at the southern edge of the glaciers in northeastern and midwestern United States. 18,000 years ago: Oldest seashells on Long Island and Cape Cod. 11,000 years ago: Glaciers retreat to just north A rock column from a Great Lakes basin. The top layer is glacial till of the St. Lawrence River. Water flows out of the (a few thousand years old) directly on top of Silurian rock, which is over 400 million St. Lawrence River. Water levels in Lake Ontario years old. (Undifferentiated layers cannot be precisely aged.) and Lake Erie suddenly drop to about the level Courtesy US Geological Survey. they are today. Vocabulary erratic boulder out-of-place boulder moraine a mound of glacial till that is deposited composed of rock that is different from the around at the edges of an advancing glacier bedrock or other area rock terminal moraine a mound of glacial till that is glacial till poorly sorted earth materials that are deposited at the front end of a glacier carried and deposited by glaciers FOSS Next Generation Glaciers—Page 2 of 8 © The Regents of the University of California Version date November 20, 2018 Can be duplicated for classroom or workshop use. Geoscenario Resources—Glaciers: Glaciologist Task Now that you have explored as a team the general story of how glaciers shaped the midwestern and northeastern United States, it is time for each of you to dive into more specialized information. The glaciologist notes focus on how glaciers form, advance and retreat, and what information glaciers can provide about past environments. Add helpful details to your notes for the Geoscenario Team Questions. Then work together and combine all the information to successfully present your story of glaciers. Questions for the Glaciologist to Consider • How do glaciers form, advance, and retreat? • What information do glaciers provide about past environments? Information Glaciers are always moving forward. A receding glacier is not moving backward; it is simply Glaciers store about 69 percent of the world’s melting faster than it is moving forward. A fresh water. Almost 10 percent of the world’s glacier that is building and moving forward faster landmass is currently covered with glaciers, than it is melting is called an advancing glacier. mostly in Greenland and Antarctica. Glacier Formation Glaciers can form when more snow falls in the winter than melts during the summer. Snow accumulates and stays year-round at high altitudes and high latitudes. After enough layers of snow accumulate, there is so much weight pushing down on the lower layers of snow that they are transformed into extremely dense layers of glacial ice. If the ice is in a mountain valley, gravity slowly pulls the dense, massive ice toward lower elevations. If it is on flat land, the weight of the ice where it is the thickest will cause the ice on the bottom to flow outward, as seen in the diagram below. This map shows how much of North America the Laurentide (or Wisconsin) Ice Sheet covered during the last glacial period. The arrows show the flow direction of the ice sheet. Courtesy USGS. Water from glaciers is constantly melting and refreezing. The water runs into cracks in the bedrock and refreezes and expands, breaking off pieces of the rock. The rocks, boulders, and other earth materials that have frozen in the ice become A glaciologist in an ice cave in the Mendenhall Glacier in Alaska. Glacial ice is so dense part of the glacier and are carried along with the that only the blue-spectrum light can escape. glacier as it moves. © Bruce Molina, Terra Photographics FOSS Next Generation Glaciers—Page 3 of 8 © The Regents of the University of California Version date November 20, 2018 Can be duplicated for classroom or workshop use. Other Interesting Facts • When the climate warmed and the glaciers began to melt, they produced millions of cubic kilometers of very cold meltwater. • Moraines from retreating glaciers formed dams that kept the meltwater from flowing south. • Towering, retreating glaciers formed ice dams that kept the meltwater from flowing north. • Snow that formed the estimated 70 million cubic kilometers of ice-age glaciers in North America came from water that evaporated from the ocean. This lowered the ocean level worldwide by 130–150 meters. Notice the layers within the glacier. Courtesy US Geological Survey Stories in the Ice • Each year, snow forms a layer of ice in a glacier. Ice cores can be drilled and removed from the A glaciologist taking a sample glacier in order to study the layers. of an ice core. • Each layer of ice can be analyzed to determine Courtesy of National what was happening during the year that the Oceanic and Atmospheric ice accumulated. Administration • Air bubbles trapped in the ice can hold stories of air temperature and atmospheric concentration of carbon dioxide (CO2 ), methane, and sulfur dioxide from volcanic eruptions. • Ice layers can also tell stories about atmospheric concentrations of volcanic ash and pollen. • Some ice cores from Antarctica provide a record of over 400,000 years. Events 20,000 years ago: Glacial ice cores indicate the beginning of a gradual warming trend. 15,000-11,000 years ago: The Laurentide Ice Sheet retreats from the northern United States. 1300-1850: Glacial ice cores show temperatures are 3–8°C (6–14°F) cooler during the 550-year period in North America and Europe. 1815-1816: Volcanic ash and sulfur dioxide gas bubbles are found in glaciers around the globe. 1850 (beginning of the industrial age): Boulders in a small pond of meltwater being carried along on top of a glacier. When the glacier melts, the boulders will be deposited in an area far from where they Ice-core data show that CO2 in the atmosphere originated. © iStockphoto/Roman Krochuk begins to increase. Vocabulary 1950: Direct measurement of the CO2 level in the atmosphere shows a more rapid increase, atmospheric CO2 concentration of carbon which continues to the present time. dioxide gas in the atmosphere ice cores cylinders of ice that have been drilled out of a glacier meltwater water from the melting glaciers FOSS Next Generation Glaciers—Page 4 of 8 © The Regents of the University of California Version date November 20, 2018 Can be duplicated for classroom or workshop use. Geoscenario Resources—Glaciers: Paleoclimatologist Task Now that you have explored as a team the general story of how glaciers shaped the midwestern and northeastern United States, it is time for each of you to dive into more specialized information.