Alaska Satellite Facility - Distributed Active Archive Center

Glacier Power – What is Glacial Calving?


Cows have calves, glaciers calve icebergs, which are chunks of ice that break off glaciers and fall into water.

Calving is when chunks of ice break off at the terminus, or end, of a glacier. Ice breaks because the forward motion of a glacier makes the terminus unstable. We call these resulting chunks of ice “icebergs.”

Icebergs can be BIG. At least one has been seen that’s as big as the state of Rhode Island!

Icebergs come in various colors. An iceberg’s color can tell us a lot about what it’s made of or where it came from.
For example:

  • White icebergs have lots of bubbles inside
  • Blue icebergs are very dense
  • Greenish-black icebergs may have calved off the bottom of a glacier
  • Darkly-striped icebergs carry moraine debris from the glacier

Icebergs in Glacier Bay

A large iceberg floating in Glacier Bay, Alaska. Photo by James Roush.
Many icebergs in Glacier Bay, Alaska. Photo by Kristina Ahlnas.

Did you know that 90 percent of an iceberg is underneath the water’s surface? Icebergs can be dangerous to ships. In April of 1912 a ship called the Titanic collided with a huge iceberg. The iceberg ripped a 90 meter hole (approximately the size of a football field) in the ship, causing it to sink. More than 1,500 people died in the accident.

Icebergs calved from tidewater glaciers are still a danger today. An iceberg over 80 kilometers long and 40 kilometers wide recently broke off from the Larsen Sea Shelf in Antarctica. Many ships sail in this area, so satellites monitor the area for any icebergs that may be in a ship’s path.

The Titanic

In the spring of 1912, the luxury passenger liner Titanic, advertised as the first iceberg-proof ship, set off on its maiden voyage, full of passengers.

On April 12 seven messages were dispatched to the Titanic, warning the ship’s crew of a huge iceberg in their path. The Titanic tried to maneuver around the iceberg, but couldn’t escape the gigantic chunk of ice.

All the passengers on the ship were alerted, and many scrambled for the lifeboats. However, there was such a panic that many boats were lowered into the sea only half full! Some boats weren’t even used at all.

Many people didn’t realize the Titanic was sinking. Some passengers were sleeping, and the band even kept playing until the boat sank. In all, 1,503 people died in the accident.

Never underestimate the power of an iceberg. If you’re ever on a boat in iceberg territory, always have a plan of escape. Be a good shipmate!

Child's Glacier Wave Warning

Seeing is believing! Look at the large rocks in the woods and picture how they arrived there.

The thunder of falling ice is a warning signal from Child’s Glacier. Heed this warning thunder — it signals an approaching glacial wave that can rise up to 20 feet when it breaks over the beach, sweeping boulders before it.

Be prepared to move to higher ground!



moraine debris

Review Questions
(some of the answers may come from the vocabulary list)

  1. Do glaciers have cows? 
  2. What are chunks of ice that break off glaciers and fall into the water?
  3. What are the three rules starting with the letter “L” that you need to do at Child’s Glacier?  
  4. Do you move to higher or lower ground when you see a glacier calving?
  5. One of the rules is to “Look” at Child’s Glacier. What can you probably see in the woods?  
  6. There are photographs taken of Child’s Glacier calving. How high did the wave reach?
  7. What town in Alaska is Child’s Glacier close to?
  8. If an iceberg had lots of bubbles inside, what color might it be?
  9. What does a darkly-striped iceberg consist of?

Brain Challenge!
What would it be like if you were in a boat and a glacier started to calve? Do you think it would rock your boat if you were right next to the glacier?

Exercise: Circle the Calving Glacier
Circle the things a calving glacier could do.

A. Cause chunks of ice to fall into the water
B. Knock down the Empire State Building
C. Knock down a person
D. Cause a glacial wave to rise over 20 feet when it breaks over the beach
E. “Moo” like a cow

Project: Think About It

Look for ragged ice debris on top of a normally smooth glacier surface. This is evidence of recent avalanching. Now think, would there be any connection between avalanche activity and the time of day? How about with time of year?

(Courtesy of Glaciers of North America, By S. Ferguson)