Clean Water: Ice [b]

I C E

Ice - comes in two varieties: permanent and transient. Both start mostly as snow. Transient ice falls in the winter and melts in the spring.

Glaciers are permanent and last throughout the year. Glaciers form where it doesn't get hot enough to melt all of the snow that falls in winter. This happens:
1) at high elevation regardless of latitude,
2) in polar areas regardless of elevation.

Fig. Ross ice shelf at the Bay of Whales, Antarctica. Photo by Michael Van Woert, NOAA.

Although there are glaciers at 10,000 feet (3,000 m) in California, there are glaciers at sea level in Alaska.

Fig. Glaciers around the world today.

Glaciers are "rivers of ice" shaping the landscape by moving slowly downhill. They push and break rocks aside. Rocks embedded in the base scrape the ground like sandpaper. Glaciers form features like Half Dome in Yosemite and steep fjords. These sharp and carved features are exposed after the glaciers retreat.

Some reservoirs of water change size and volume over time. Over the last million years, glaciers have come and gone numerous times. During warm times, reservoirs of ice shrink and the oceans grow. During times of maximum glaciation, sealevel was lower by 125 meters. Although the size of any water reservoir can change over long time periods, it is a concern when the change happens over human time scales.

Fig. Rivers of glacial ice in Alaska, Taku Glacier. Photo courtesy of NOAA.

Permanent ice doesn't always sit on the ground. Water can also seep into the ground and freeze permanently. This is permafrost.

Buildings on permafrost ground require special engineering because warm objects can sink into the ground.

Snowpack is a useful way to package water. Glaciers and permafrost are inaccesible water resources. However transient ice in snowpack is a very useful water resource. In semi-arid environments like southern California, rivers flow best just after rains and not at our convenience. It's like a tap we can't control.

But snow doesn't melt right away. In California the snowpack melts through the summer, supplying our dams with water throughout the dry months as we use it.

Fig. Measuring the thinkness of the Sierra snowpack in California. Will there be enough water through summer? This measurement will tell. Photo courtesy of David Jones, UC Santa Barbara.

You might think we could build dams to trap all the runoff in winter, but where it rains a lot, there's too much to store. It would overflow the capacity of our dams and reservoirs. Snowpack allows us to spread the flow our over the year.

If you're from the midwest, the east, or Alaska, you'd be amazed at the view of a southern California river. Many California rivers are dry river beds during the summer, full of rocks and gravel.

PART 1
Water on Earth
• Overview
• Stores of Water
• Infinite cycle:
finite resource
• Sculpting the earth
• What's left to drink?
Quiz
Glossary
Resources
Teacher's guide
Information Sources

• Activity Ice.1
Investigate: Was your home covered by glaciers during the last major glaciation?

Starting points:
Global land environments since the last interglacial
Maps showing distribution of terrestrial ecosystems and glacial ice now and in the past, from around the world.

• Activity Ice.2
News:
Shrinking snow pack
CBS News

• Activity Ice.3
Technology:
Alyeska Pipeline Service Company homepage
See how the Trans Alaska Pipleine System is constructed in a permafrost situation.