What’s The Difference Between A Glacier And An Iceberg?

I am grateful for this platform because it allows me to provide little science lessons periodically. Many people rarely think much about basic science once school days have passed. While watching the the game show America Says on Game Show Network recently, a contestant said something that inspired this article. I believe the question asked the team to name things that you might see in Alaska. The team captain said something along the lines of, “We all love the movie Titanic so we are going to go with a glacier.” That was the correct answer, however, it was actually an iceberg that sank the Titanic. What’s the difference between a glacier and an iceberg?

As an atmospheric scientist and meteorologist, I am familiar with little things like this. People routinely ask me about meteors (I don’t study them) or tsunamis (an ocean process not an atmospheric one). However, I had not consider that some people may not think about or know the difference between an iceberg and a glacier. Let’s start with formal definitions and then dig a bit deeper.

According to the U.S. Geological Survey (USGS) website, a glacier is, “a large, perennial accumulation of crystalline ice, snow, rock, sediment, and often liquid water that originates on land and moves down slope under the influence of its own weight and gravity.” One of my favorite family trips was to Glacier National Park a few years ago in Montana. We went to catch a glimpse of a glacier since most of them in the park have disappeared over the past century.

The National Oceanic and Atmospheric Administration (NOAA) website points out that an iceberg is “ice that broke off from glaciers or shelf ice and is floating in open water.” While it is likely that any chunk of ice floating in the ocean might be called an iceberg, the NOAA website explains that to be considered an iceberg, the height must exceed 16 feet above sea level, have a thickness between 98 and 164 feet, and cover an area greater than 5,382 square feet. Icebergs can also take on many shapes including tabular (steep sides and flat tops), domes, and spires. Roughly 88 percent of an iceberg is below the water line according to a U.S. Coast Guard website.

While many glaciers are found in alpine or land-based regions, some glaciers extend to the ocean. At times, pieces of a glacier can break off into the water. At that point, it may be considered an iceberg if it meets aforementioned criteria. In February 2020, NASA Earth observing satellites observed the Pine Island Glacier producing new icebergs. According to the NASA Earth Observatory website, the Pine Island Glacier in Antarctica is one of the world’s fastest retreating glaciers. Kathryn Hansen writes, “It is a normal part of life for the floating ice from huge glaciers to fracture near the seaward edge and calve off as icebergs.”

As climate changes, the dynamics of glaciers and icebergs will be important indicators for climate scientists. Recent data suggests that mountain glaciers worldwide have experienced mass losses for almost three decades. It is exactly why Glacier National Park was on my bucket list.

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