Glaciers similar to those in the Tierra Del Fuego fjords
and Global warming's effect on glaciers
The information below is for anyone planning on going to Tierra Del Fuego
and also for those interested in Global Warming.
FAQ and Myths
Common Questions and Myths about Glaciers
Questions:
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.
Myths:
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.
http://ak.water.usgs.gov/glaciology/FAQ.htm
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
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
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.
http://members.aol.com/scipioiv/glacierparts.html
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
http://members.aol.com/scipioiv/glmain.html
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
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.
The Arctic, Antarctica and Cape Horn 
