An iceberg is a large mass of freshwater ice that has broken off, or calved, from a glacier or an ice shelf and is floating in open water. Alaska is one of the world’s most dynamic locations for glacial activity, making it a source for these impressive ice formations. The state’s extensive coastline and numerous tidewater glaciers ensure that icebergs are a common sight in its fjords and bays throughout the warmer months.
The Process of Glacial Calving
Icebergs are created through calving, which occurs when a glacier’s terminus meets a body of water. Most icebergs originate from tidewater glaciers, which flow all the way to the sea. Calving is driven by gravity, fracture mechanics, and the buoyant force of the seawater surrounding the ice front.
Water depth at the glacier’s face is a major factor, as deeper water allows for greater buoyancy forces to lift and fracture the ice. These glaciers often build up a moraine shoal, a pile of sediment beneath the water, which can temporarily stabilize the ice front. When the glacier retreats from this shoal into deeper water, its stability is significantly reduced, often leading to a period of rapid, accelerated calving.
Icebergs are composed of compressed freshwater ice that formed from snow over thousands of years. As the glacial ice accelerates toward the terminus, stress fractures and crevasses weaken the structure. Eventually, the pressure from the flowing ice and the upward lift from the water causes a large section to break away, crashing into the fjord as a new iceberg.
Primary Locations for Iceberg Viewing
The best opportunities to view icebergs are concentrated in the regions of Alaska where tidewater glaciers are most active.
- Glacier Bay National Park and Preserve is perhaps the most famous destination, with Margerie and Johns Hopkins Glaciers being primary sources of iceberg production. Visitors typically experience these areas via authorized cruise ships or smaller tour vessels.
- Prince William Sound, accessible from towns like Whittier and Valdez, is another rich area for iceberg observation. Glaciers such as the Columbia Glacier calve into the sound, filling its deep fjords with floating ice. This area is popular for guided boat tours and kayaking excursions.
- Kenai Fjords National Park, near Seward, offers dramatic viewing opportunities in Aialik Bay and Northwestern Fjord. Glaciers like Aialik and Holgate regularly shed ice into the water, creating dense collections of icebergs. Day cruises departing from Seward offer the most reliable way to witness these calving events.
- A more remote option is Tracy Arm Fjord, south of Juneau, which leads to the twin Sawyer Glaciers. The narrow fjord is often filled with blue icebergs, which can sometimes block the passage of larger vessels.
Understanding Iceberg Size Classifications
Icebergs are officially classified by size to standardize terminology for navigation and observation.
Growler
The smallest category is the Growler, which is typically defined as a piece of ice less than one meter high above the sea surface and smaller than a car. Growlers are especially hazardous to small boats because they are difficult to spot in the waves and often pose the greatest hidden threat to navigation.
Bergy Bit
The next size up is the Bergy Bit, a fragment generally between one and five meters in height and roughly the size of a small house. These medium-sized pieces are large enough to be clearly visible and tracked by vessels. Both growlers and bergy bits are often the result of larger icebergs breaking apart as they melt and drift.
Iceberg
A true Iceberg is the largest classification, defined as any piece of ice that stands more than five meters above the water line. These towering masses can be massive, with the vast majority of their volume—up to 90 percent—hidden beneath the surface. Knowing these classifications helps visitors and mariners accurately describe the specific ice formations they encounter in Alaskan waters.