Discussion

What are Glaciers?

Most simply, glaciers are permanent ice fields that move.

An accumulation of unmelting snow over many years builds up enough mass that its weight compresses the snow below the surface into ice. Movement occurs when the total mass is enough for gravity to begin to pull the ice down mountain slopes (valley glaciers) or when the mass grows so great and thick that its gigantic weight squeezes its boundaries to expand outward (continental glaciers or ice sheets).

Continental Glaciers

The vast glaciers that the ice ages were known for were continental glaciers. The map below shows the size of the North American ice sheets during the last major ice age about 15,000 years ago.

There was so much ice piled up on land in an earlier ice age 20,000 years ago that the sea level was 400 feet lower than it is today. That allowed people to migrate from Asia to North America because those continents were connected by a land bridge where the Bering Strait is located today.

Continental glaciers still exist today in Greenland and Antarctica, the surfaces of which are almost totally covered with them. Here is a map of Antarctica's glaciers.

Antarctica's ice sheet averages about 1.3 miles thick; about 3 miles thick at its deepest point. It contains about 7.2 million cubic miles of ice, 90% of the world's total. In comparison, Greenland's ice sheet contains about 0.7 million cubic miles of ice. If all of Antarctica's ice were to melt, worldwide sea levels would rise about 200 feet. The ice shelves shown on the map are areas where glacial ice has been pushed off of land and is floating on the ocean, though still attached to the land-based glacier.

Nearly all of the world's glaciers are melting, including Antarctica's. Edges of the ice shelves are breaking off to float away from the continent as gigantic ice bergs. This reduces some of the resistance that slows down the movement of the glaciers toward the sea. A more realistic worst case estimate for sea level rise from melting Antarctician ice is 60 feet if nothing is done to abate global warming. The Totten Glacier catchment area is where thinning is happening most rapidly. In the last thirty years, the global average sea level has risen 3.5 inches. Because of the rotation of the Earth, the rise is greater at the equator where the sea level rise is more than 5.9 inches.

That may not seem like much, but it is devastating for low-laying countries like Tuvalu and the Maldives, and shorelines around the world are at risk of significantly changing, displacing many millions of people. At Tuvalu whose highest elevation is only about 15 feet above sea level, formerly dry coastal roads are now routinely flooded during the greatest high tides.

Acreage that used to be used for agriculture is becoming saturated with salt water, and fresh water supplies are threatened. The island nation may become uninhabitable within a few decades--one estimate is 12 years. Tuvalu has recently negotiated an agreement with Australia to allow a limited number of Tuvaluans to migrate there annually and have a pathway to citizenship. The ideal would be for them to have some area of their own where they could preserve their culture.

Estimates are that 80% of the Maldives, another low-laying island nation, will become uninhabitable by 2050 because of sea level rise. 

Valley Glaciers

Valley glaciers are much more common, with estimates that there are as many as 200,000 of them worldwide. It is believed that there exist many more that have not yet been discovered. The reason is explained below. If all of them were to melt, it would raise the sea level an estimated 1.6 feet. The last few decades have seen a significant amount of melting in almost all of them.

The photo above is an aerial view of the famous Columbia Glacier in Alaska's Prince William Sound. Its front is about three miles across. It is one of the fastest moving glaciers in the world. By moving, it is meant that the ice flows downward from its alpine origins. Here is a link to brief time lapse video that shows what is meant when glaciers are sometimes called rivers of ice.

https://youtu.be/TWGR6FxFlt8

The Columbia Glacier's ice's rate of travel is more than a foot a day. Note that though the ice in the video is moving forward, the front of the glacier is not changing much. That is because as the glacial ice moves forward, the ice at the front is melting, breaking off (calving), and/or evaporating at a rate that closely matches the forward flow of the ice. If that rate of loss at the front is slower than the ice is moving forward, the glacier's front advances. If the rate of loss is faster than the ice is moving forward, the glacier's front retreats.

Here is a photo of a portion of the front of the Columbia Glacier as of this summer.

The height of the ice cliffs at the front are up to 400 feet above the water line and it extends about 400 feet below it. Ice burgs as large as 10 story buildings routinely calve off of the front.

Looking at the aerial photo of the Columbia Glacier above, it can be seen that it begins with several different glaciers that merge together to form one large glacier. The smaller glaciers that join the main one are called tributary glaciers.

Those dark streaks are called moraines; rock and soil deposits referred to as glacial till. As glaciers move, they grind away rock from the mountains and carry the material with it. Some of it is deposited at the sides of the glacier as it moves. This build-up of material is called a lateral moraine. When tributary moraines merge, the lateral moraines join to become medial moraines that continue to be dragged forward as the ice flows.

f the front of a glacier is stationary--i.e., the falling away or melting of ice in the front occurs at the same rate as the ice moves forward--glacial till is deposited at the front, forming a terminal moraine. The glacier in the photo below has retreated, but it can be seen that for some period of time, it had spread out as it emerged from the valley, then stopped long enough to deposit enough glacial till to create the low terminal moraine around its outer perimeter. Then it retreated a bit before remaining stationary again for a longer period, shown by the much higher mound a little behind the outer ring.

Some glaciers, like the Columbia Glacier, terminate at the ocean. These are called tidewater glaciers. Tidewater glaciers still leave glacial till at the front, but unless the front remains stationary long enough, the deposits are left underwater. The Columbia Glacier has a substantial terminal moraine, but it is underwater about 12 miles away from where the front is today.

Because of global warming, the Columbia Glacier began to retreat in 1980. Though global warming started the process, much of the retreat to its current position is due to the shape of the sea floor under the glacier's leading edge. When the Columbia Glacier's front is fully grounded, it is believed that its retreat will either slow down or stop. It may even start to slowly advance again.

As the Columbia Glacier retreated, it left behind several tributary glaciers which are now independent glaciers on their own. The photo below shows one of them.

The dark notch at the waterline on the left side of the glacier is about the size of the excursion boat the photo was taken from this summer.

Glaciers shape the landscape in more ways than from the moraines they leave behind. For one thing the shape of the valleys they cut because of the grinding away of rock on the bottoms and sides is different from river-cut valleys.

Sometimes, the walls of the valleys that glaciers cut are nearly vertical, creating what are known as hanging cliffs. One of the most well-known examples of this is Yosemite Valley which has several spectacular waterfalls.

Yosemite Valley went through several stages on the way to becoming what it is today. The illustrations below show those stages. The first stage is what is called the pre-Tahoe glacier, the next is the Tioga glacier, and the final stage is glacial Lake Yosemite, formed by the end of the valley being dammed up by the terminal moraine from the Tioga glacier. The valley floor became flat when the lake filled up with silt.

As glaciers move with its load of ground down rocks and silt, it scrapes the rocks on the mountain sides it moves past, leaving behind areas that have a polished look. If you drive to Yosemite Valley on CA 41 from Fresno, you can see examples of glacial polish along the roadside. The photo below was taken at a different location, but this is what it looks like.

One of the features of glaciers that some may have heard about without knowing what it is is blue ice.

The natural color of water is blue. That is easily seen in aerial photos of lakes and oceans. When ice freezes, however, it appears to be white. That is because it has imbedded within it huge numbers of microscopically tiny air bubbles. Ice under hundreds of feet if not under miles of ice and snow is under immense pressure; enough that those microscopically tiny bubbles are forced out, leaving behind nearly pure water ice; the color blue.

For those interested, there is a lot more that can be learned about glaciers and their effect on our planet. This illustration shows just a little of it.

Glacierets

Not all glaciers are huge things. Many are quite small. Still, if it is ice and it moves naturally, it is a glacier. A glacieret is a very small glacier. The reason that we don't have a better estimate of how many glaciers there are in the world is that it is sometimes hard to know if something is a glacier or is just a snowfield that persists year after year. Mountains have lots of those.

Until recently, it was believed that there were no glaciers in Japan. That didn't stop researchers from looking. Japan has three areas high enough and rugged enough to be thought of as Japanese alps, and they have plenty of permanent snow fields. Taking measurements over several years with ground penetrating radar, three glacierets were recently identified buried under permanent snowfields. The discovery was confirmed by a consortium of scientists in 2023.

They are all located in Japan's Hida mountains, located in what is called Japan's Northern Alps on the big island of Honshu.

Artwork

I have no Japanese artwork with glaciers to show, but my demonstration painting this week has a whale in it with a glacier in the background. For that reason, I thought a photo of a whale would be appropriate. This photo is actually of a whale-shaped fountain spouting water. It is located in Juneau, Alaska.