The Lambert Glacier in East Antarctica is widely recognized as the longest glacier in the world, stretching roughly 400 kilometers (250 miles) from its headwaters to the point where it feeds into the Amery Ice Shelf. The answer gets slightly complicated, though, because glacier length depends on how you define “one glacier.” The Lambert flows together with the Mellor and Fisher glaciers before merging into the Amery Ice Shelf, and some measurements of the full Lambert-Fisher system extend even further. By any standard, it is an enormous river of ice draining about 7% of the entire East Antarctic ice sheet.
Where the Lambert Glacier Is and Why It’s So Large
The Lambert Glacier sits in East Antarctica, carving a path between exposed mountain peaks called nunataks before converging with the Mellor and Fisher glaciers at the rear of the Amery Ice Shelf, the third largest ice shelf on the continent. The three tributary glaciers narrow to widths as slim as 30 kilometers where they flow between the mountains, then spread out dramatically as they reach the shelf.
East Antarctica holds the bulk of the continent’s ice, and the Lambert system acts as a major drainage channel for it. Between 2008 and 2015, the system discharged more than 60 gigatons of ice per year into the Amery Ice Shelf. To put that in perspective, a single gigaton of ice is roughly enough to fill 400,000 Olympic swimming pools.
How Fast the Lambert Moves
NASA velocity maps show the Lambert Glacier moves at 400 to 800 meters (roughly 1,300 to 2,600 feet) per year across most of its length, with a slight slowdown in the middle section. Smaller glaciers feeding into it flow more slowly, at 100 to 300 meters per year. Once the ice reaches the Amery Ice Shelf, it accelerates to 1,000 to 1,200 meters per year as the sheet spreads out and thins.
These speeds are moderate by Antarctic standards. Some outlet glaciers in West Antarctica move several kilometers per year. But the Lambert’s sheer width and depth mean it transports a massive volume of ice even at relatively modest speeds.
Is the Lambert Glacier Shrinking?
Unlike many glaciers around the world, the Lambert-Amery system has been remarkably stable. Observations and modeling studies confirm that it has maintained a steady state since the 1960s, when systematic measurements began using ground surveys, GPS, and eventually satellite tracking. A 2016 mass balance assessment estimated a slight positive balance of about 3.1 gigatons per year, meaning the system was actually gaining a small amount of ice rather than losing it.
Modeling of the system’s future under various warming scenarios suggests the grounding line, where the glacier lifts off the bedrock and begins to float, will remain stable and won’t trigger the kind of rapid retreat seen elsewhere in Antarctica. Increased snowfall in the region may actually offset ice lost through faster flow. Over the next 500 years, simulations project the system could either add a tiny amount to global sea levels or subtract up to about 117 millimeters’ worth by storing more ice. That makes the Lambert system a potential buffer against sea level rise, not a contributor to it.
The Longest Glacier Outside Antarctica
Outside the polar regions, the title goes to the Fedchenko Glacier in northern Tajikistan. It stretches 77 kilometers (47 miles) as it winds northward from the heart of the Pamir Mountains toward the border with Kyrgyzstan. That’s impressive for a mountain glacier, but still less than a fifth of the Lambert’s length. NASA has described Fedchenko as relatively stable compared to many mid-latitude glaciers, though it sits in a region where warming temperatures are gradually reshaping ice cover.
In Alaska, the Bering Glacier holds the record as the longest glacier in North America at 196 kilometers (122 miles). The Bering is also one of the largest glaciers in the world by area. Alaska is also home to the Hubbard Glacier, which has been steadily advancing into Disenchantment Bay since measurements began in 1895. Hubbard’s growth runs counter to the trend of thinning and retreating glaciers nearby. Its unusually large catchment basin high in the Saint Elias Mountains feeds it more snow than it loses, and a buildup of rocky debris at its front edge acts like a stabilizing wall, letting the ice push forward more easily.
Why Measuring Glacier Length Is Tricky
Ranking glaciers by length is less straightforward than it sounds. Scientists need to determine where a glacier begins and ends, which requires defining the boundaries of its accumulation zone (where snow packs into ice) and its terminus (where it melts or breaks off). For massive Antarctic glaciers that feed into ice shelves, the endpoint is especially debatable: do you stop at the grounding line, or include the floating ice shelf?
A 2014 study published in The Cryosphere developed an automated method for calculating glacier center lines globally, using surface slope and distance to glacier edges. The researchers noted that measurements of very small glaciers carry a degree of ambiguity, but even large glaciers can produce different length figures depending on methodology. This is why you’ll sometimes see different numbers for the Lambert Glacier depending on the source, and why some lists rank glaciers by area rather than length. The World Glacier Monitoring Service, for instance, ranks the world’s largest individual glaciers by area rather than length, placing the Seller Glacier on the Antarctic Peninsula first at 7,018 square kilometers.
Regardless of which measurement method you use, the Lambert Glacier holds its position at the top. No other single glacier on Earth comes close to its length.