Glaciers are dynamic rivers of ice that flow slowly but relentlessly from high-elevation accumulation zones toward the sea. The question of which glacier holds the title of the world’s longest draws attention to the extremes of polar geography. Measuring these colossal ice formations requires sophisticated science, particularly in the remote, harsh environment of Antarctica.
Identifying the World’s Longest Glacier
The longest known glacier system on Earth is the Lambert-Fisher Glacier/Ice Stream System, located in East Antarctica. This colossal feature drains a substantial portion of the East Antarctic Ice Sheet toward the coast. The grounded portion, known as the Lambert Glacier, measures approximately 400 kilometers (250 miles) in length and flows into the Amery Ice Shelf, a massive floating extension.
The entire flow line, extending from the inland drainage divide to the outer edge of the floating ice shelf, is estimated to be 1,470 kilometers (913 miles). The system is a complex network of ice movement, with the Fisher Glacier being a significant tributary that merges into the Lambert Glacier. This combined system makes it the largest single-outlet glacier drainage basin in the world.
Defining and Measuring Glacial Length
Determining the precise length of a glacier of this magnitude is complicated because the definition of a “glacier” is not always simple in the Antarctic context. A true glacier is a mass of ice moving over land, distinct from an ice shelf, which is a thick, floating slab of ice attached to the landmass. The Lambert-Fisher system is technically an ice stream, a region of an ice sheet that flows significantly faster than the surrounding ice.
Measurement depends heavily on where the grounded ice ends and the floating ice begins. Scientists define this boundary as the grounding line, which can move with the tides and is often buried beneath kilometers of ice. Glaciologists rely on remote sensing techniques, such as Synthetic Aperture Radar Interferometry (InSAR), to detect the vertical flexure of the ice surface caused by ocean tides to pinpoint this line.
The use of satellite imagery, including Landsat and radar data, allows researchers to employ feature tracking to measure the ice’s velocity and direction of flow. This methodology helps define the inland boundary, or drainage divide, where the snow and ice begin their journey toward the sea. Because of these methodological challenges, the quoted length can vary depending on whether the floating ice shelf component is included in the total measurement.
The Significance of the Lambert-Fisher System
The Lambert-Fisher system is far more than a record-holder; it is the largest single drainage route for the East Antarctic Ice Sheet (EAIS), the largest mass of ice on Earth. This system transports ice accumulated over a catchment area of approximately 1.6 million square kilometers, accounting for about 16% of the EAIS. The ice flux, or the volume of ice entering the Amery Ice Shelf through the grounding line, is estimated to be nearly 20 gigatons per year.
The flow of the grounded glacier is buttressed, or held back, by the massive Amery Ice Shelf. This floating shelf acts as a brake, slowing the movement of the inland ice. Its stability is of great importance to global sea-level rise projections because if the ice shelf were to thin or collapse, the upstream ice flow would accelerate, potentially increasing the rate at which grounded ice is discharged into the ocean.
Monitoring the flow rate and mass balance of the Lambert-Fisher system serves as an important barometer for the overall stability of the EAIS. Recent studies suggest that the system’s mass balance is currently near equilibrium, meaning the ice accumulation roughly equals the ice loss. However, the rate of net accumulation has been observed to be decreasing, underscoring the necessity of continued surveillance in a warming climate.