Alaska is one of the world’s most active regions for iceberg production, yielding countless floating chunks of glacial ice. An iceberg is defined as a large piece of freshwater ice that has broken off a glacier or ice shelf and is floating in open water, typically measuring more than 16 feet across. Alaska’s vast network of over 27,000 glaciers, particularly those that terminate in the sea, constantly feeds icebergs into the coastal waters.
The Mechanism of Formation: Glacial Calving
The creation of icebergs is primarily driven by glacial calving. Calving occurs when a glacier terminates in a body of water, such as a fjord or the ocean, and large pieces of ice fracture and separate from the main ice mass. This process represents the most significant form of ice loss for water-terminating glaciers. Tidewater glaciers, which flow directly into the sea, are the most prolific iceberg producers in Alaska.
Tidewater glaciers accelerate as they approach the water, enhancing their response to changes in water depth and temperature. When the glacier’s terminus retreats into deeper water, the loss of support causes instability, leading to an increased rate of calving. The resulting icebergs are composed of compressed freshwater ice, originating from thousands of years of accumulated snowfall.
This glacial ice differs fundamentally from sea ice because it is formed on land from precipitation, not the freezing of saltwater. The freshwater origin means the ice is denser and purer, often displaying a striking blue color. Calving events can range from small, constant discharges to massive collapses that send chunks of ice into the water. The size and frequency of these events are influenced by the depth of the water at the glacier face.
Primary Regions for Iceberg Observation
Alaska’s geography, defined by steep coastal mountains and deep fjords, creates ideal conditions for viewing icebergs.
Glacier Bay National Park
Glacier Bay National Park is a premier location, home to active tidewater glaciers like Margerie Glacier, which regularly calve into the bay’s waters. The floating ice masses here range widely in size and drift throughout the long, deep fjords.
Prince William Sound
Prince William Sound, easily accessible from Anchorage, contains numerous tidewater glaciers. Excursions often target College Fjord and Harriman Fjord, where glaciers like Columbia and Harvard actively shed ice. The concentration of icebergs in these protected waters makes for consistent viewing opportunities, often alongside marine wildlife.
Kenai Fjords and Tracy Arm
Kenai Fjords National Park features the vast Harding Icefield feeding numerous glaciers, with five reaching tidewater. Glaciers like Holgate and Aialik are known for their frequent calving, creating a continuous stream of floating ice. Southeast Alaska also offers viewing in Tracy Arm Fjord, where the Sawyer Glaciers produce immense icebergs.
Defining Characteristics of Alaskan Icebergs
Alaskan icebergs are typically smaller in scale than the colossal tabular icebergs calved from the ice shelves of Antarctica. The majority of floating glacial ice seen in Alaskan waters is classified as smaller pieces: “bergy bits” and “growlers.” Growlers are ice chunks less than one meter above the water’s surface, while bergy bits are between one and five meters tall.
The color of Alaskan icebergs is often a deep, luminous blue. This hue results from the ice’s high density and the absence of trapped air bubbles, which scatter all colors of light equally and make regular ice appear white. The dense, compacted glacial ice absorbs the longer wavelengths of light, leaving only the blue spectrum to be reflected back.
Alaskan icebergs generally have a shorter lifespan compared to their Arctic counterparts due to the relatively warmer surrounding waters. They melt more quickly, often dissolving completely within a few weeks of calving. Occasionally, the ice contains streaks of brown or black sediment, which are layers of rock and dust incorporated into the glacier as it scraped along the land.