The information below is for anyone planning on going to Tierra Del Fuego and also for those interested in Global Warming.
Common Questions and Myths about Glaciers
1. Why are there glaciers?
Glaciers form where more snow falls than melts over a period of years, compacts into ice, and becomes thick enough to begin to move. That is, a snow patch becomes a glacier when the deepest layers begin to deform due to the weight of the overlying snow and ice.
2. Why are glaciers blue?
Because the red (long wavelengths) part of white light is absorbed by ice and the blue (short wavelengths) light is transmitted and scattered. The longer the path light travels in ice, the more blue it appears.
2.1 So... why is snow white?
Light does not penetrate into snow very far before being scattered back to the viewer. However, the next time you are in an igloo, notice that it is blue inside. You can also poke a stick into some snow, shade the area around the hole, and look deep into the snowpack. The light that has traveled some distance through the snow will be enhanced in blue.
3. Is glacier ice colder than regular ice?
No - indeed, all of the physical, thermal and electrical properties of "regular icebox ice" and glacier ice are identical: density, viscosity, heat of fusion, latent heat, heat capacity, dielectric constant, thermal conductivity, absorption, emissivity, etc. The few small differences in characteristics are solely due to grain size differences (see 3.1). NOTE: High pressure forms of ice with different properties have been produced in laboratory experiments, but none occur naturally on earth, not even at the base of the Antarctic or Greenland ice sheets.
3.1. But doesn't glacier ice last longer in drinks!!!???
Yes - a little, but only because the ice crystals are larger. Crystals melt from the outside and large crystals expose less surface area per unit volume of ice; therefore, ice with larger crystals melts more slowly.
4. When a glacier retreats, does the ice go back up the valley?
No - like water, ice flows down its surface gradient, is rarely pushed up, and never goes back up valley. Retreat occurs when melting or calving removes ice more quickly than glacier flow replenishes it.
5. How many glaciers are in Alaska?
There is no certain answer. There are 616 officially named glaciers in Alaska (see USGS Geographic Names Information System online data base), and many more unnamed glaciers. The Alaska Almanac estimates that Alaska has 100,000 glaciers -- that's a pretty good estimate.
6. How many glaciers in Alaska have floating termini (or terminuses and which is it)?
None - all the calving glaciers in Alaska fill their fjords completely to the bed. Ice shelves (floating ice at a glacier's terminus) occur only on the "cold" glaciers (see Myth number 4) in Antarctica and Greenland. In Alaska, parts of some retreating calving glaciers are close to floating (such as Columbia and Portage Glaciers).
(Both "termini" and "terminuses" are correct terms. I prefer "termini" because it's easier to pronounce.)
7. What makes a glacier different from an ice cube or ice in a hockey rink?
A glacier must:
* be formed from natural atmospheric precipitation (snow)
* move by internal deformation due to its own weight
NOTE: these criteria exclude "aufeis" which is the technical term for the "glaciering" or "icing" that form during winter where emerging ground water freezes, often encroaching onto highways and trails.
8. How thick are glaciers?
A good guess is that the ice thickness is about one-half of the surface width of the glacier. Although few glaciers have been measured, the measured thicknesses range from a few tens of meters for small glaciers to about 1,500 meters for the largest glaciers in Alaska.
1. Iceworms are a joke originated by gold rush poet Robert Service (see The Ballad of the Ice-Worm Cocktail).
They are real - they are annelid worms (class Oligochaeta); several species are recognized. Also, there are several insects and algae that live on the surfaces of glaciers.
2. Alaska was covered by glaciers during the Great Ice Age (Pleistocene).
No - interior Alaska was a grassland refuge habitat for a number of plant and animal species during the maximum glaciation.
3. Today's glaciers are leftovers from the ice age and Glacier ice is "really old."
Sort-of and no - we must distinguish between glaciers and the ice in glaciers. Like the difference between rivers and the water in rivers: it takes a few weeks for water to travel the full length of the Mississippi river; however there has been a Mississippi River for thousands of years. Likewise, glaciers have existed in the mountains ever since the ice age, but glacier flow moves the snow and ice through the entire length of the glacier in 100 years or less. So, most of the glacier ice in Alaska is less than 100 years old! Therefore, most of the glacier ice is not ice-age leftovers.
NOTE: There is "really old" ice near the bases of the Greenland and Antarctic ice sheets and in a few special places in the world's mountains.
3.1 What about the mammoths and giant bison found in ice?
The remains of prehistoric animals are indeed found in ice, but not glacier ice. Frozen fossil animals are found in permafrost. Permafrost may be many tens of thousands of years old.
3.1.a But, the Copper-Age "Iceman" found during 1991 in the European Alps was "in a glacier."
Special circumstances preserved the Iceman. His body was not destroyed when the site was over-ridden by a glacier because it was near the edge of the glacier in a protective bedrock depression. Had he truly been in a glacier, he would have been ground to flour.
4. Glacier ice is very cold.
Not really - most of the glacier ice in Alaska is only a few tenths of a degree below the melting temperature, except for a surface layer a few meters thick that is cooled during winter. As a consequence, most glaciers in Alaska are not frozen to their beds. These glaciers are referred to as "temperate" glaciers. Glaciologists refer to a glacier as a "cold" glacier if it is more than a few degrees below the freezing temperature throughout most of its thickness.
Dissecting a Glacier
There are several sizes and types of Glaciers, differing mainly on locale and size. Thus, all types have several features and regions in common.
Glaciers in Motion
If you get around 20 meters (65 feet) of material, the sheer weight of the mass of snow, firn and glacial ice causes the lowest portions to deform into sliding layers, and the glacier can then begin to flow. Often, a layer of meltwater also helps reduce friction, and allows for smoother movement of the glacier. The topmost layers of ice do not deform, and can crack and split when ice moves underneath. This is known as the zone of fracture, and as I will shortly explain, makes walking on a glacier dangerous.
Thus the glacier flows downhill,scouring the terrain in its path. Even on a level surface, a glacier will act like a mound of pudding.. will deform and ooze out on its sides. In general, though, glaciers flow like rivers. The rate of this flow varies from 0.01-0.1 meter/day for the large continental glaciers to 0.1-2 meters/day for a typical alpine glacier. During a surge, a period of rapid glacier movement, an alpine glacier can flow at the rate of 50-100 meters a day. Imagine that. A glacier adding to it's area the length of a football field in a single day. So much for glacial slowness, huh?
As you can see, this picture is a nice dissection of a typical glacier. The topmost portion of the Glacier, at its coldest portions, is known as the zone of accumulation. It is here that the snow exceeds melting,and glacial ice can accumulate as I discussed before. Further down the glacier is the zone of ablation or wastage. Here, there is more melting than accumulation in a year. Finally, the glacier has a terminus, the furthermost extent of the glacier. The equilibrium line is the point on a glacier where the amount of snow falling is equal to the amount of snow melting. Note that, due to the change in seasons, these regions, and the terminus of the glacier can fluctuate between winter and summer.
The flow of glacial ice can, in the aptly named zone of fracture, produce vertical to nearly vertical, wedge-shaped cracks called crevasses. These cracks may range in size from a few centimeters to over 10 meters in width and up to about 40 meters in depth. Becoming injured by falling into a crevasse is a hazard for anyone travelling across the surface of a glacier, especially because crevasses may be hidden by snow and difficult to detect. Crevasses most commonly form where the ice flows over irregularities in the bedrock beneath and along the sides of the ice. Ice falls form where a glacier descends abruptly and produce abundant crevasses. Walking on a glacier should NEVER be done alone, and not without a mountaineer experienced in such conditions. Note that this zone of fracture extends into the glacier only until the point that the weight of the ice causes it to deform and flow. This actually is very similar to the principles of plate tectonics and how deep in the earth's crust earthquakes can and cannot occur.
Types of Glaciers
Glaciers can be divided into 2 general types, Alpine or Mountain Glaciers, those Glaciers which originate on a mountain or in a mountain range, and the Continental Glaciers, the large masses of Glacial ice in Greenland and Antarctica. There are several variants and sub categories of each.
Alpine Glaciers are the glaciers most people are familiar with from photographs. Although they are much smaller than the continental ones, they are much more scenic in my opinion, and also much more accessible to viewing by the public. A trip to Mount Rainier is a lot more accessible than a trip on a research boat to Antarctica. A Valley Glacier is the prototypical river of ice that I like to talk about. They often form in stream valleys, and originate meltwater streams themselves at their terminus.
A Cirque Glacier is a glacier in a depression, usually at the head of valleys. Should a cirque glacier extend itself far enough, it can grow out of the depression, and become a valley glacier.
A Niche Glacier is a very small glacial form which exists in a shallow hollow on a steep mountain slope.
Piedmont Glaciers are glaciers which extend from their mountain origin all the way onto a plain.
And even these sub categories can be further divided. A confluent glacier, for example, is the merging of 2 or more glaciers, for example. Click on this link for an excellent photograph of this type of phenomenon. A tidewater glacier is a valley glacier which reaches the sea, and thus calves small icebergs, but is often subject to being eroded at the terminus by wave action. Many of the more accessible Alaskan glaciers are of this variety.
Continental Glaciers are the big boys of the Glacier set. They contain most of the glacial ice in the world, and can be hundreds and even thousands of meters thick. During the last ice age, the continental glaciers reached out like a white amoeba to cover 32% of the total land area on the planet.
Continental glaciers are subdivided into 2 main types based on their size: the relatively small ice caps, and the mammoth ice sheets.
Further ice features include the ice shelf, an ice cap or ice sheet which extends out over the water, such as the Antarctic Ross Ice Shelf. An iceberg, of course, is a piece of an ice sheet or ice shelf which floats out into the oceans. Such an iceberg, of course, was responsible for the sinking of the Titanic.
Glaciers, Rivers of Ice
This website is devoted to my interest in the rivers of ice known as glaciers. It was inaugurated as part of the requirements of a course I have taken in the geology of National Parks.
In the meantime, here, you can explore this fascinating world of the rivers of ice in a virtual manner, and even find information on National Parks which feature glaciers, or landscapes once carved by them. You will also therein the geology of the various types of glaciers, from what is a glacier to how they work, to features in landscapes created by glaciers.
I recommend going through the pages in order, even if you do know some geology. In my research to put up this site, I learned lots of interesting information I had never even suspected about glaciers. Perhaps you'll be pleasantly surprised as well.
Rivers of Ice Main Menu
* Glacier Facts
* What is a Glacier, anyway?
* Why doesn't the snow in my backyard become a Glacier? How do they form?
* Composition of a typical Glacier and the types of Glaciers. How a glacier moves.
* Where are the World's Glaciers? Where have they been?
* What geologic features are formed by Glacier action?
* What do Glaciers have to do with Global Warming?
* Where can I see a Glacier or what Glaciers have done?
* Glacial Inspirations ..Websites to visit and Books to read to get into a Glacial Mood
Glaciers and Glaciation
Glaciers constitute much of the Earth that makes up the cryosphere, the part of the Earth that remains below the freezing point of water. Most glacial ice today is found in the polar regions, above the Arctic and Antarctic Circles. While glaciers are of relatively minor importance today, evidence exists that the Earth's climate has undergone fluctuations in the past, and that the amount of the Earth's surface covered by glaciers has been much larger in the past than in the present. In fact, much of the topography in the northern part of North America, as well as in the high mountain regions of the west, owe their form to erosional and depositional processes of glaciers. The latest glaciation ended only 10,000 years ago.
Definition of a glacier
A glacier is a permanent (on a human time scale, because nothing on the Earth is really permanent) body of ice, consisting largely of recrystallized snow, that shows evidence of downslope or outward movement due to the pull of gravity.
Types of Glaciers
* Mountain Glaciers - Relatively small glaciers which occur at higher elevations in mountainous regions.
* Smallest of these occupy hollows or bowl-shaped depressions on sides of mountains (cirque glaciers).
* As cirque glaciers grow larger they may spread into valleys and flow down the valleys as valley glaciers. Paths these valley glaciers take are controlled by existing topography.
* If a valley glacier extends down to sea level, it may carve a narrow valley into the coastline. These are called fjord glaciers, and the narrow valleys they carve and later become filled with seawater after the ice has melted are fjords.
* If a valley glacier extends down a valley and then covers a gentle slope beyond the mountain range, it is called a piedmont glacier.
* If all of the valleys in a mountain range become filled with glaciers, and the glaciers cover then entire mountain range, they are called ice caps.
* Ice Sheets: (Continental glaciers): are the largest types of glaciers on Earth. They cover large areas of the land surface, including mountain areas. Modern ice sheets cover Greenland and Antarctica. These two ice sheets comprise about 95% of all glacial ice currently on Earth. They have an estimated volume of about 24 million km3. If melted, they contain enough water to raise sea level about 66m (216 ft.). This would cause serious problems for coastal cities (L.A., NY, Washington DC, New Orleans, Miami, SF etc). The Greenland ice sheet is in some places over 3000 m (9800 ft) thick and the weight of ice has depressed much of the crust of Greenland below sea level. Antarctica is covered by two large ice sheets that meet in the central part along the Transantarctic Mountains. These are the only truly polar ice sheet on earth (North Pole lies in an ocean covered by thin layer of ice.
* Ice Shelves: Ice shelves are sheets of ice floating on water and attached to land. They usually occupy coastal embayments, may extend hundreds of km from land and reach thicknesses of 1000 m.
Glaciers can also be classified by their internal temperature.
* Temperate glaciers - Ice in a temperate glacier is at a temperature near its melting point.
* Polar glaciers - Ice in a polar glacier always maintains a temperature well below its melting point.
The Formation of Glacial Ice
Glaciers can only form at latitudes or elevations above the snowline, which is the elevation above which snow can form and remain present year round. The snowline, at present, lies at sea level in polar latitudes and rises up to 6000 m in tropical areas. Glaciers form in these areas if the snow becomes compacted, forcing out the air between the snowflakes. As compaction occurs, the weight of the overlying snow causes the snow to recrystallize and increase its grain-size, until it increases its density and becomes a solid block of ice.
Changes in Glacier Size
A glacier can change its size by Accumulation, which occurs by addition of snowfall, compaction and recrystallization, and Ablation, the loss of mass resulting from melting, usually at lower altitude, where temperatures may rise above freezing point in summer. Thus, depending on the balance between accumulation and ablation during a full season, the glacier can grow or shrink.
Movement of Glaciers
Glaciers move to lower elevations under the force of gravity by two different processes:
* Internal Flow - called creep, results from deformation of the ice crystal structure - the crystals slide over each other like deck of cards. This type of movement is the only type that occurs in polar glaciers, but it also occurs in temperate glaciers. The upper portions of glaciers are brittle, when the lower portion deforms by internal flow, the upper portions may fracture to form large cracks called crevasses. Crevasses occur where the lower portion of a glacier flows over sudden change in topography (see figure 12.11 on page 314 of your text).
* Basal sliding - meltwater at base of glacier reduces friction by lubricating the surface and allowing the glacier to slide across its bed. Polar glaciers are usually frozen to their bed and are thus too cold for this mechanism to occur.
The velocity of glacial ice changes throughout the glacier. The velocity is low next to the base of the glacier and where it is contact with valley walls. The velocity increases toward the center and upper parts of the glacier.
Glaciation: is the modification of the land surface by the action of glaciers. Galciations have occurred so recently in N. America and Europe, that weathering, mass wasting, and stream erosion have not had time to alter the landscape. Thus, evidence of glacial erosion and deposition are still present. Since glaciers move, they can pick up and transport rocks and thus erode. Since they transport material and can melt, they can also deposit material. Glaciated landscapes are the result of both glacial erosion and glacial deposition.
Glacial Erosion (note: most of this material will be presented as slides in class)
* Small scale erosional features
* Glacial striations - long parallel scratches and grooves that are produced at the bottom of temperate glaciers by rocks embedded in the ice scraping against the rock underlying the glacier (see figure 12.18 in your text).
* Glacial polish - rock that has a smooth surface produced as a result of fined grained material embedded in the glacier acting like sandpaper on the underlying surface.
* Landforms produced by mountain glaciers
* Cirques - bowl shaped depressions that occur at the heads of mountain glaciers that result form a combination of frost wedging, glacial plucking, and abrasion. Sometimes small lakes, called tarns occur in the bottom of cirque.
* Glacial Valleys - Valleys that once contained glacial ice become eroded into a "U" shape in cross section. Stream erosion, on the other hand, produces valleys that are "V" shaped in cross section.
* Arêtes - If two adjacent valleys are filled with glacial ice, the ridges between the valleys can be carved into a sharp knife-edge ridge, called an arête.
* Horns - Where three or more cirques are carved out of a mountain, they can produce a sharp peak called a horn .
* Hanging Valleys - When a glacier occupying a smaller tributary valley meets the larger valley, the tributary glacier usually does not have the ability to erode its base to the floor of the main valley. Thus, when the glacial ice melts the floor of the tributary valley hangs above the floor of the main valley and is called a hanging valley. Waterfalls generally occur where the hanging valley meets the main valley.
* - Fjords are narrow inlets along the seacoast that were once occupied by a valley glacier, called a fjord glacier.
* Landforms produced by Ice Caps and Ice Sheets
* Abrasional features - The same small-scale abrasional features such as striations and glacial polish can occur beneath ice caps and ice sheets, particularly in temperate environments.
* Streamlined forms - The land surface beneath a moving continental ice sheet can be molded into smooth elongated forms called drumlins.
Since glaciers are solid they can transport all sizes of sediment, from huge house-sized boulders to fine-grained clay sized material. The glacier can carry this material on its surface or embedded within it. Thus, sediment transportation in a glacier is very much different than that in a stream. Thus, sediments deposited directly from melting of a glacial can range from very poorly sorted to better sorted, depending on how much water transport takes place after the ice melts. All sediment deposited as a result of glacial erosion is called Glacial Drift.
* Ice Laid Deposits
* Till - nonsorted glacial drift deposited directly from ice. Till consists of a random mixture of different sized fragments of angular rocks in a matrix of fine grained, sand- to clay-sized fragments that were produced by abrasion within the glacier. This fine-grained material is often called rock flour because it is really ground up rock. A till that has undergone diagenesis and has turned into a rock is called a tillite.
* Erratics - a glacially deposited rock or fragment that now rests on a surface made of different rock. Erratics are often found many kilometers from their source, and by mapping the distribution pattern of erratics geologists can often determine the flow directions of the ice that carried them to their present locations.
* Moraines - are deposits of till that have a form different from the underlying bedrock. Depending on where it formed in relation to the glacier moraines can be:
* Ground Moraines - these are deposited beneath the glacier and result in a hummocky topography with lots of enclosed small basins.
* End Moraines and Terminal Moraines are deposited at the low elevation end of a glacier as the ice retreats due to ablation (melting)
* Lateral Moraines are deposits of till that were deposited along the sides of mountain glaciers.
* Medial Moraines - When two valley glaciers meet to form a larger glacier, the rock debris along the sides of both glaciers merge to form a medial moraine. These black streaks in an active glacier, as well as the deposits left behind after the ice melts are called medial moraines.
* Glacial Marine drift - Glaciers that reach the oceans or even lakes, may calve off into large icebergs which then float on the water surface until they melt. Upon melting, the rock debris that they contain becomes immediately deposited on the sea floor or lakebed as an unsorted chaotic deposit. Sometimes single large rock fragments fall out on the floor of the water body, and these are called dropstones.
* Stratified Drift - Glacial drift can be picked up and moved by meltwater streams which can then deposit that material as stratified drift.
* Outwash Plains - Streams running off the end of a melting glacier are usually choked with sediment and form braided streams, which deposit poorly sorted stratified sediment in an outwash plain. These deposits are often referred to as outwash.
* Outwash Terraces - If the outwash streams cut down into their outwash deposits, the banks from river terraces called outwash terraces.
* Kettle Lakes - If depressions form underneath a glacier and remain after the glacier is melted then water filling these depressions become small lakes where fine-grained sediment is deposited. The state of Minnesota is called the land of a thousand lakes, most of which are kettle lakes.
* Kames and Kame Terraces. Streams and lakes forming on top of stagnant ice may deposit stratified sediment on top of the glacier. When the glacier melts these deposits are set down on the ground surface. The former lake deposits become kames, and the former stream deposits become kame terraces.
* Eskers - Eskers are long sinuous ridges of sediment deposited by streams than ran under or within a glacier. The sediment deposited by these streams becomes an esker after the ice has melted.
The last glaciation ended about 10,000 years ago. But the period between 10,000 years ago and 3 my ago (Pleistocene epoch) was a time of many glacial and interglacial ages. During this period sea level fluctuated because:
* during glaciations the continental land masses were depressed by weight of ice.
* during glacial periods much sea water was tied up in glaciers so sea level was lower.
* during interglacial periods sea level was higher due to melting of the ice.
* during interglacial periods land that were covered with ice during a glaciation are uplifted due to removal of the weight of the ice.
Based on evidence from glacial deposits and glacial erosion features geologists have been able to document at least 4 glaciations during the Pleistocene. But recent studies of deep-sea sediments and dating of these deposits suggest that there were at least 30 glaciations that occurred during the Pleistocene. This evidence comes from studies of fossils found in deep-sea sediment cores, and what they tell us about ocean surface temperatures in the past. The results come from studies of the isotopes of oxygen.
* Oxygen has two major isotopes, 18O, which is considered heavy, and 16O, which is considered light. Both of these isotopes are stable and non-radiogenic, so their ratio is constant through time.
* Because 16O is lighter, it is preferentially evaporated with sea water from the oceans, and thus gets concentrated in the water that eventually falls on the continents as rain or snow. Because of this, 18O gets concentrated in ocean water.
* During constant climatic conditions the 16O lost to evaporation returns to the oceans by rain and streams, so that the ratio of 18O to 16O (18O / 16O) is constant.
* But, during a glaciation, some of the 16O gets tied up in glacial ice and does not return to the oceans. Thus during glaciations the 18O / 16O ratio of sea water increases.
* During an interglaciation, on the other hand, the 16O that was tied up in glacial ice returns to the oceans causing a decrease in the 18O / 16O ratio of seawater.
Thus, we expect that during glaciations the 18O / 16O ratio in seawater will be high, and during interglaciations the 18O / 16O ratio in seawater will be low.
Since organisms that live in the oceans extract Oxygen from seawater to form their carbonate (CO3-2) shells, measuring the 18O / 16O ratio in the shells of dead organisms gives a record of past ocean temperatures. The record for the past two million years. This suggests about 30 glaciations separated by interglaciations during the past 2 million years.
During the last 1 million years it appears that each glacial - interglacial cycle has lasted about 100,000 years, but earlier cycles were about 40,000 years long.
Other periods of glaciation are known from the geologic record, mainly from preserved glacial striations and tillites (consolidated till). The earliest recognized glaciation occurred about 2.3 billion years ago, but at least 50 other glaciations are recognized to have occurred during the Paleozoic era.
Causes of Glacial Ages
In order to understand what causes these cycles of glacial - interglacial episodes we need a much better understanding of what causes global climate changes. Because human history is so short compared to the time scales on which global climate change occurs, we do not completely understand the causes. However, we can suggest a few reasons why climates fluctuate.
* Long term variations in climate (tens of millions of years) on a single continent are likely caused by drifting continents. If a continent drifts toward the equator, the climate will become warmer. If the continent drifts toward the poles, glaciations can occur on that continent.
* Short-term variations in climate are likely controlled by the amount of solar radiation reaching the Earth. Among these are astronomical factors and atmospheric factors.
* Astronomical Factors -
* Variation in the eccentricity of the Earth's orbit around the sun has periods of about 400,0000 years and 100,000 years.
* Variation in the tilt of the Earth's axis has a period of about 41,000 years.
* Variation in the way the Earth wobbles on its axis, called precession, has a period of about 23,000 years.
* The combined effects of these astronomical variations results in periodicities similar to those observed for glacial - interglacial cycles.
* Atmospheric Factors- the composition of the Earth's atmosphere can be gleaned from air bubbles trapped in ice in the polar ice sheets. Studying drill core samples of such glacial ice and their contained air bubbles reveals the following:
* During past glaciations, the amount of CO2 and methane, both greenhouse gasses that tend to cause global warming, were lower than during interglacial episodes.
* During past glaciations, the amount of dust in the atmosphere was higher than during interglacial periods, thus more heat was likely reflected from the Earth's atmosphere back into space.
* The problem in unraveling what this means comes from not being able to understand if low greenhouse gas concentration and high dust content in the atmosphere caused the ice ages or if these conditions were caused by the ice ages.
* Changes in Oceanic Circulation - small changes in ocean circulation can amplify small changes in temperature variation produced by astronomical factors.
* Other factors
* The energy output from the sun may fluctuate.
* Large explosive volcanic eruptions can add significant quantities of dust to the atmosphere reflecting solar radiation and resulting in global cooling.
Prof. Stephen A. Nelson Geology 111
Tulane University Physical Geology
Glaciers and Global Warming
It's seems kind of obvious, on the face of it. When things get warmer, ice melts, right? So, if global warming was really happening, glaciers all over the world should, local variations aside, be generally in retreat, moving back up the mountains, getting smaller.
And this is precisely what is happening, all over the world. Oh,local variations do exist, and some glaciers have shown surges, but in football terms, the Glaciers' defense keeps giving up first downs to Global Warming.
One of the most dramatic retreats is in one of our very own National Parks, Glacier Bay in Alaska. When Captain Cook, discoverer of the Hawaiian Islands, visited Glacier Bay in the late 18th century, ice from the glaciers choked the inlets of the bay so thoroughly that he could not enter them.
Especially in the last 40 years, the Glaciers of Glacier Bay have retreated dramatically. In the case of some of the Glaciers of Glacier Bay, the tidewater glaciers have moved back as much as 70 miles. While it is true that tidewater glaciers such as the major Glaciers of Glacier Bay National Park are somewhat different than alpine glaciers, and may not be the best indicators of climate change, even the non tidewater glaciers of Glacier Bay have shown retreat.
The recovery of the five thousand year old 'ice man' from the Alps, too, is an indication that glacier lengths are shortening rapidly and severely. In general, Glaciers everywhere are simply melting away, like Frosty the Snowman.
Perhaps the biggest concern, from an environmental standpoint, is the fate of the Greenland and Antarctic ice sheets. Even if, as scientists are now realizing, that greenhouse gasses are only part of the global warming, should it continue for whatever reason, the ice sheets could very well show significant melting...dumping their water into the ocean...a LOT of water. As you can guess, this would necessarily create a raising of global ocean sea level. Beachfront property in Philadelphia and Dallas, anyone?
The map to the right illustrates this point quite convincingly, don't you think? You can also see from this map, the dramatic drops in sea level when Ice Ages are in full force. There is nothing normal about our present coastlines...they are just between the two extremes. Many of the islands of Micronesia, some with elevations above sea level in the tens of feet, could completely cease to exist, were the Glaciers to disappear. Manhattan Island would become a new Venice. http://members.aol.com/scipioiv/glacierwarming.html
March 20, 2002
Large Ice Shelf in Antarctica Disintegrates at Great Speed
By ANDREW C. REVKIN
A satellite image shows the disintegration of an ice shelf about the size of Rhode Island on the eastern side of the Antarctic Peninsula.
Satellite images over little more than a month show the disintegration of an ice shelf on the eastern side of the Antarctic Peninsula.
Rhode Island-size piece of the floating ice fringe along a fast-warming region of Antarctica has disintegrated with extraordinary rapidity, scientists said yesterday.
The loss of floating ice does not contribute to rising sea levels, just as melting ice cubes floating in a glass do not cause it to overflow. But the researchers said this was the first time in thousands of years that this part of Antarctica - the east coast of its arm-shaped peninsula - had seen so much ice erode and temperatures rise so much.
While it is too soon to say whether the changes there are related to a buildup of the "greenhouse" gas emissions that scientists believe are warming the planet, many experts said it was getting harder to find any other explanation.
"With the disappearance of ice shelves that have existed for thousands of years, you rather rapidly run out of other explanations," said Dr. Theodore A. Scambos, a glaciologist at the National Snow and Ice Data Center at the University of Colorado, which has been monitoring the loss of ice in the Antarctic along with the British Antarctic Survey.
Other parts of Antarctica have experienced different trends, including a cooling of the continent's interior in recent decades.
The latest ice breakup occurred in the Larsen B ice shelf, which has probably existed since the last ice age. "There's no evidence of any period in the last 12,000 years where there was open water in the area that has now been exposed," Dr. Scambos said.
For years, researchers hiking on the ice and using satellites have been watching pieces of the shelf slowly break away, but the disintegration over the last month was on a vastly greater scale, several experts said. "The speed of it is staggering," said Dr. David Vaughan, a glaciologist at the British Antarctic Survey.
Starting in February, satellites recorded the event as the ice sheet fragmented into thousands of floes.
Scientists say the likely culprit is rapidly warming summer air temperatures. Along that part of the peninsula, temperatures have risen 4.5 degrees in five decades, and hundreds of small ponds of meltwater have formed on the surface of the Larsen shelf and others nearby.
The surface water migrates into tiny cracks in the ice, steadily deepening and widening them until the monumental structure starts to fall apart, Dr. Scambos said.
There's plenty of evidence that our planet's glaciers and ice sheets are in a phase of melting. But there's at least one type of glacier that moves to its own beat. Tidewater glaciers.
Wednesday, December 29, 1999
NASA/Goddard Space Flight Center
This is Earth and Sky. Many of the planet's glaciers have been seen in recent years to be melting -- possibly in response to a warming climate. But one type of glacier advances and retreats on its own cycle. We spoke with Dr. Dorothy Hall, a glaciologist with NASA's Earth Science Enterprise, about tidewater glaciers.
(Tape) A tidewater glacier is a glacier that ends in the ocean or in a fjord. It will advance for about a thousand years or so -- slowly. At some point, probably having to do with the depth of the fjord, a sudden retreat will be triggered. The glacier will retreat for about one hundred years or so, calving icebergs along the way. When it gets to a shallow part of the fjord or back to land, the cycle will begin again.
JB: Tidewater glaciers don't make good subjects to study the effects of climate warming -- because they advance slowly and retreat rapidly. I think that the tidewater glaciers are surely moving in response to climate and climate change at some level. We don't understand what that is, and they don't appear to be changing very much according to short-term climate change.
Small Warming Could Jeopardize Water Supplies
Just one or two degrees of global warming could have dramatic impacts on water resources across western North America, a new study suggests. The researchers, from the National Center for Atmospheric Research and elsewhere, were surprised by the size of the effect generated by only a small rise in temperature.
Australian Glacier Loss Accelerates
Australia's glaciers are melting. The shrinking of Australia's little-known glaciers on remote, sub-Antarctic Heard Island in the Indian Ocean reveals global warming now stretches from the tropics to the edge of Antarctica. "The recession of many glaciers during the past 50 years has been unprecedented in modern times for Heard Island," said glaciologist Andrew Ruddell of with the Australian Antarctic Division.
Icelandic Glacier, Biggest in Europe, is Disintegrating
Europe's biggest glacier is about to disintegrate. The mighty Breidamerkurjökull in southern Iceland is breaking apart and will slide into the north Atlantic in the next few years. The imminent destruction of this gigantic river of ice demonstrates starkly that global warming is now making a serious impact on the northern hemisphere, threatening to melt ice caps and raise sea levels round the world.
Kilimanjaro's Glacial Retreat Confirms Warming
The vanishing of the seemingly perpetual snows of Kilimanjaro that inspired Ernest Hemingway, echoed by similar trends on ice-capped peaks from Peru to Tibet, is one of the clearest signs that a global warming trend in the last 50 years may have exceeded typical climate shifts and is at least partly caused by gases released by human activities, a variety of scientists say.
Himalayan Ice Cores Show Last 50 years Hottest in Millennium
More evidence that the Earth is warmer than at any time in the past 1,000 years has come from ice cores in a glacier on the "roof" of the world. Himalayan ice cores provide convincing evidence that the past 50 years ­p; and the 1990s in particular ­p; have been the warmest of the past millennium.
North Pole Melts after 50 million-year Freeze
The North Pole is melting. The thick ice that has for ages covered the Arctic Ocean at the pole has turned to water, recent visitors there reported yesterday. At least for the time being, an ice-free patch of ocean about a mile wide has opened at the very top of the world, something that has presumably never before been seen by humans and is more evidence that global warming may be real and already affecting climate. The last time scientists can be certain the pole was awash in water was more than 50 million years ago.
Worldwatch: Earth's Meltdown Accelerates
Around the world, ice sheets and glaciers are melting at a rate unprecedented since record-keeping began. The Worldwatch Institute has compiled reports from across the globe, which show that the melting accelerated during the 1990s - the warmest decade on record. Glaciers and other ice features are especially sensitive to temperature shifts and scientists suspect the enhanced melting is among the first observable signs of human-induced global warming.
Himalayan Glaciers May Disappear by 2035
Glaciers in the Himalayas are receding faster than in any other part of the world, causing anamolous floods, mudslides and river overflows in a traditionally dry part of the world. At present rates, they are likely to disappear in the next 40 years.
Melting of Earth's Glaciers Accelerates
The vast majority of the earth's glaciers have been melting for at least two decades. The most recent measurements indicate that the so-called rate of "glacial retreat" is accelerating rapidly.
Greenland Ice Sheet Thins Faster than Expected
The southern half of the Greenland ice sheet, the second largest expanse of land-bound ice earth after Antarctica, has shrunk substantially in the last five years. Experts have said for some time that a warming atmosphere has caused many mountain glaciers around the world to shrink. But until now, they have not known what was happening to the Greenland ice cap. While five years is too short a period to mark a trend, the new findings provide the first precise evidence that it, too, is diminishing.
Glacial Retreat Faster than Previously Thought
All of the glaciers in Glacier National Park in Montana will be gone in the next 50 to 70 years, according to researchers measuring global melting rates. The Montana glaciers and others are melting more quickly than scientists had
Melting Glaciers Threaten Alaskan Ships
The Columbia Glacier in Alaska's Prince William Sound is disgorging more than one million tons of ice a day into shipping lanes outside Valdez, posing a threat to the more than 600 tankers laden with Alaskan crude oil that traverse the lanes each year
Antarctic Glaciers Shrink Rapidly
Retreat of Antarctic glaciers accelerates, as temperatures rise by 5 degrees Fahrenheit.
EARLY WARNING SIGNS
OF GLOBAL WARMING
Glaciers exist on all continents except Australia and at virtually all latitudes from the tropics to the poles. Mountain glaciers, such as those that exist at higher elevations in the mid-latitudes and tropics, are particularly sensitive indicators of climate change. The volume of ice in a glacier-and correspondingly its surface area, thickness, and length-is determined by the balance between inputs (accumulation of snow and ice) and outputs (melting and calving). As climate changes, the balance between inputs and outputs may change, resulting in a change in thickness and the advance or retreat of the glacier. Temperature, precipitation, humidity, wind speed, and other factors such as slope and the reflectivity of the glacier surface all affect the balance between inputs and outputs. Most glaciers in the world, however, are more sensitive to temperature than to other climatic factors (Fitzharris, 1996).
There is widespread evidence that glaciers are retreating in many mountain areas of the world. Since 1850 the glaciers of the European Alps have lost about 30 to 40% of their surface area and about half of their volume (Haeberli and Beniston, 1998). Similarly, glaciers in the New Zealand Southern Alps have lost 25% of their area over the last 100 years (Chinn, 1996), and glaciers in several regions of central Asia have been retreating since the 1950s (Fitzharris, 1996; Meier, 1998). For three glaciers in the US Pacific Northwest, the seven-year average rate of ice loss was higher for the period since 1989 than for any other period studied (Hodge et al., 1998). Glacial retreat is also prevalent in the higher elevations of the tropics. Glaciers on Mt. Kenya and Kilimanjaro have lost over 60% of their area in the last century (Hastenrath, 1991; Hastenrath and Greischar, 1997), and accelerated retreat has been reported for the Peruvian Andes (Mosley-Thompson, 1997).
By contrast, losses in the Arctic have been less pronounced (0-6% in area and 1-14% in volume), partly because those glaciers are much colder and the extra meltwater refreezes in the ice mass (M. Meier, pers. comm.). Although there is considerable variability at the regional and local scales and over shorter time periods, the overall global signal shows mass loss and retreat of glaciers during the last century. For the period 1884­p;1978, the mean global glacial retreat corresponds to a calculated warming of about 0.7°C per century (Oerlemans, 1994).
Global compilations indicate that the wastage of mountain glaciers during the last century has raised sea level by between 0.2 to 0.4 mm/yr, or roughly 20% of the observed change (e.g,. Warrick et al., 1996; Dyurgerov and Meier, 1997). By 2100, sea level is estimated to rise by an additional 46 to 58 cm, with an estimated total range of 20 to 86 cm (Warrick et al., 1996). Over half of the change will likely be from thermal expansion of ocean water, another 30% from melting of mountain glaciers, and 10% from melting of parts of the Greenland ice sheet (Gregory and Oerlemans, 1998). If future climate change is consistent with model projections, up to one quarter of the presently existing mountain glacier ice will disappear by 2050 (Fitzharris, 1996).
The shrinking of glaciers will likely have a significant socioeconomic impact in some mountain regions, though the exact local impacts remain uncertain and will vary. Regions that lose major parts of their glacier cover will experience alterations in hydrology. The glaciers will initially provide extra runoff from melting; but as the ice diminishes, the runoff will wane. Also, because revegetation of terrain is slower at high altitudes, deglaciated areas will be subject to erosion and decreased stability, heightening the need to protect buildings, roads, communication links, and other structures. For areas dependent on tourism, uncertain snow cover during peak winter sports seasons, natural hazards such as rock and ice falls, or loss of scenic beauty are of particular concern. An example of the type of scenario that could become more frequent occurred during the warm summer of 1998, when a ski area in the Tyrolian Alps was forced to close a lift after melting ice dislodged rocks and soil, destabilizing the peak (GECR, 1998).
Chinn, T. 1996. New Zealand glacier responses to climate change of the past century. New Zealand Journal of Geology and Geophysics 39, 415-428.
Dyurgerov, M. B., and M. Meier. 1997. Mass balance of mountain and sub-polar glaciers: A new global assessment for 1961-1990, Arctic and Alpine Research, 29 (4), 379-391.
Fitzharris, 1996. The cryosphere: Changes and their impacts. In Climate Change 1995: The Science of Climate Change, (Eds J. T. Houghton, L. G. M. Filho, B. A. Callander, N. Harris, A. Kattenberg, and K. Maskell), 241-265, Cambridge University Press, Cambridge, UK.
GECR, 1998. Melting glacier destabilizes Austrian peak. Global Environmental Change Report, vol. X, no. 22, p. 6.
Gregory, J.M. and J. Oerlemans, 1998. Simulated future sea-level rise due to glacier melt based on regionally and seasonally resolved temperature changes. Nature 391, 474-476.
Haeberli, W., and M. Beniston. 1998. Climate change and its impacts on glaciers and permafrost in the Alps. Ambio 27, 258-265
Hastenrath, 1991. Climate Dynamics of the Tropics. Kluwer Academic Publishers, Dordrecht, Netherlands, 488 p.
Hastenrath, S and L. Greischar, 1997. Glacier recession on Kilimanjaro, East Africa, 1912-89. Journal of Glaciology 43 (145), 455-459.
Hodge, S.M., D.C. Trabant, R.M. Krimmel, T.A. Heinrichs, R.S. March, and E.G. Josberger, 1998. Climate variations and changes in mass of three glaciers in western North America. Journal of Climate 11 (9), 2161-2179.
Meier, M., 1998. Land ice on Earth: A beginning of a global synthesis. Unpublished transcript of the 1998 Walter B. Langbein Memorial Lecture, American Geophysical Union Spring Meeting, Boston, MA, 26 May 1998.
Mosley-Thompson, E. 1997. Glaciological evidence of recent environmental changes. Annual Meeting of the Association of American Geography, Fort Worth, Texas.
Oerlemans, J., 1994. Quantifying global warming from the retreat of glaciers. Science 264, 243-245.
Warrick, R. A., C. L. Provost, M. F. Meier, J. Oerlemans, and P. L. Woodworth, 1996. Changes in sea level, in Climate Change 1995: The Science of Climate Change, 359-405,
(Eds JT Houghton, LG Meira Filho, BA Calander, N Harris, A Kattenburg, and K Maskell), Cambridge University Press, Cambridge.
Glaciology on the World Wide Web ­p; An excellent resource with links to sources of glaciology images and data, publications and research, and glaciology organizations. http://www-nsidc.colorado.edu/glaciology/
World Glacier Inventory ­p; Data from over 67,000 glaciers around the world, including glacier location, area, length, orientation, elevation, and classification of type. http://www-nsidc.colorado.edu/NSIDC/CATALOG/ENTRIES/G01130.html
Diaz, H.F., M. Beniston, and R.S. Bradley, 1997. Climatic Change at High Elevation Sites, Kluwer Academic Publishers, Dordrecht, Netherlands, 298 p.
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