14 Glaciers Glaciers are rivers of ice that move down-slope, usually from highlands or mountainous areas, to the sea. They are important agents of erosion, transportation and deposition. They have played a major role in shaping the landscape of the Burren, and much of the Northern Hemisphere that was covered by ice during the last Ice Age (>12,000 years ago). Glaciers form when winter snowfall exceeds summer ice melt. This can happen within a fraction of a degree Celsius - and so glaciers are very sensitive indicators of changes in climate. Glacier June 19 th, 2005 Water Glacier Margin Since 1850, when scientific monitoring of the world s glaciers began, many glaciers are retreating consistently decade by decade. The total surface area of glaciers on Earth has decreased by 50% since 1850. This phenomenon is affecting glaciers at all latitudes and longitudes and has been attributed to global warming. The process has increased dramatically since 1995. July 7 th, 2003 May 12 th, 2001 Retreat of the Helheim Glacier, Greenland (2005, 2003, 2001) Grosser Glacier, Switzerland The most significant global effect of glacial retreat is a rise in global sea levels. The current projected rise in sea level due to glacial retreat is 0.27 to 0.5 m by 2050, and 0.8 to 1.3 m by 2100; this is considered by many to be a conservative estimate. Cities that would face serious flooding include London, New Orleans, Shanghai, Rio de Janeiro, Buenos Aires, Cairo, Mumbai, Tokyo, Lagos, Bangkok, New York and Los Angeles. The total population living in low-lying areas at risk is 640 million people.
15 Approximately The Burren during the last ice age 1.8 million years ago, an ice age began during which most of Ireland was covered by glaciers. The last stage of this ice age ended 12,000 years ago. Some rocks at the base of the ice sheet were pushed along under the weight of the ice and as they moved they scratched the underlying bedrock. When you examine the flat surface of the bedrock at several localities in the Burren, you will see such scratches, known as glacial striations. If you put a compass along the line of the scratches you can see that they are facing in a WNW-ESE direction. You can therefore assume that the ice moved in this direction. Looking west towards Black Head As the glaciers moved from southwest County Galway over the Burren they smoothed the north-facing slopes of the Burren s hills. This is clearly visible on the smooth slopes of Black Head. The glaciers also removed weathered shale rocks from the land s surface; plucked blocks of limestone from the south-facing slopes of the hills and left scratches (striations) on the exposed limestone bedrock. As the ice sheets moved over the Burren, they bulldozed and eroded the surface of the underlying rock. The moving ice carried along with it all the loose sediments, shattered stones, rocks and boulders that it picked up along its route. Striations on limestone bedrock When the temperature warmed up and the ice began to melt much of this material was dropped or deposited on the landscape. Deposited glacial material includes erratics, glacial till (up to 20 m thick in some valleys), drumlins and moraines. Like the glacial striations, the drumlins and moraines indicate the path taken by some of the most recent ice sheets as they moved from southwest County Galway over north Clare. They moved from the north-east and westwards out over the Atlantic Ocean, as indicated in the map below. Terrain map of the Burren, showing the direction of movement of the most recent ice sheets.
16 When Glacial deposits in the Burren the temperature increased approximately 12,000 years ago, the last ice age ended. As the ice melted it dropped its load of sediment, rocks and stones. This load was dropped in different ways and created different features on the landscape which are still visible today. Common glacial depositional features on the Burren include erratics, glacial till, drumlins and moraines. Erratics Erratics are pieces of rock that have been transported from their original location by moving ice, and were deposited when the ice melted. The most obvious erratics in the Burren are those that are several metres wide, but there are also many smaller, pebble- or cobble-sized erratics. Limestone erratic in the Burren Some erratics in the Burren appear raised off the adjacent pavement on what are called pedestals. These pedestals show that the pavement surrounding the erratics has been lowered by dissolution since the last glaciation, but the pavement underneath the erratic has been protected from the rain and has not been lowered. The height of the pedestals allows us to calculate how fast the limestone surface is being lowered by dissolution - 1 cm every 1,000 years. This means the hills of the Burren will disappear in less than 3 million years! Erratics being exposed at the edge of a glacier in Canada as the ice melts Most erratics in the Burren region are of limestone, and so came from the Burren itself. There are, however, erratics of other rock types: granite erratics are common along the north coast of the Burren and sandstone erratics are scattered throughout the area. The nearest source of granite is the Galway granite to the north. This tells us that the ice sheets that passed over the Burren came from the north. The sandstone erratics could have come from Slieve Aughty mountains to the east, or from the erosion of the delta sandstones that once covered the Burren. Erratics occur at up to 200 m above sea level in the Burren region, indicating that the ice sheet that covered the area was at least a couple of hundred metres thick. Granite erratic on the Flaggy Shore
Granite Geological map of the area A Siltstone/ shale B Limestone Sandstone Drumlins Drumlins are small, low, rounded hills that make the landscape look like a gently rolling blanket. These low hills were formed at the end of the last Ice Age when the great ice sheets that covered Ireland were melting. These features were first recognised in Ireland; the word drumlin comes from the Irish droimnín or small hill. The drumlins are not made of rock - instead, they are made of till - mixed-up deposits of boulders, pebbles, and soil. They are rounded in shape because they were moulded or streamlined as the ice moved over them. C D E Drumlin in the Burren (Turlough Valley) F G Glacial till (Aughinish Island) A: Limestone erratic at Poulnabrone B: Ice shattered limestone erratic in Burren National Park C: Granite erratic at Doolin Point D: Conglomerate erratic at Lough Bunny E: Limestone erratic at Doolin Point F: Granite erratic at Lough Bunny G: Granite erratic at Flaggy Shore
Melting ice and sea level change 17 Background Contrary to common perception, the melting of floating sea ice does not affect global sea levels. Ice has a lower density than water and so melts to a smaller volume. Therefore the melting of sea ice and icebergs will not contribute to rising sea levels. If, however, continental ice sheets melt, global sea levels could rise by many metres and much of today s continents could be flooded. The melting of sea ice can lead to melting of continental ice. If sea ice melts, less sunlight will be reflected from the Earth s surface and the oceans will warm, eventually raising temperatures enough for continental ice sheets to melt. If this happens, there will be a huge increase in the amount of freshwater entering the oceans. This will reduce the salinity of the world s oceans and affect ocean current patterns. As ocean currents transfer heat from warm areas to colder parts of the world (e.g. the Gulf Stream), a change or shutdown of these currents will result in severe cooling in many parts of the world. Before undertaking the following activity, participants should be aware that (1) there are large ice caps on Greenland and Antarctica; and (2) water expands as it freezes (and so water takes up less space than ice) Activity Material: Two 500ml vessels (e.g. glass beaker) One tin of beans/peas ( to act as the continents) Two rulers Warm water Ice cubes Blu-tak student worksheets Activity: Part One: Introduce the fact that much of the Arctic Ocean is frozen and so are the seas around Antarctica. This activity investigates if there will be a change in sea level if floating sea-ice melts.. To set up the experiment for sea ice melting: Participants fill one 500 ml vessel roughly half-way with warm water. Crushed ice is added to raise the water level by 1 or 2 centimetres. The crushed ice imitates floating sea ice. With a ruler participants measure and record the level of water in the beaker When the ice has melted completely, the level of water is measured and recorded again. Part Two: Introduce the fact that Antarctica and Greenland are covered by ice up to 3 km thick in places. This activity investigates how melting land ice could affect global sea level. To set up the experiment for land ice melting: Participants place a tin of beans in the centre a vessel. The vessel is then filled with water to a level close to the lid of the tin. (The tin represents the continents) With a ruler participants measure and record the level of water in the beaker Crushed ice is placed on top of the tin of beans. (The crushed ice imitates continental ice sheets, such as on Greenland). When the ice has melted completely, the level of water is measured and recorded again. Participants can record their results on the worksheet.