Jakobshavn Glacier Deep Dive
Jakobshavn Isbrae — known in Greenlandic as Sermeq Kujalleq, meaning southern glacier — is by almost every measure the most consequential single glacier on Earth outside the Antarctic ice sheet. It drains approximately 6.5 percent of the Greenland Ice Sheet's total area through a single fjord on the island's west coast, near the town of Ilulissat (formerly Jakobshavn) at roughly 69 degrees North latitude. It is the fastest large glacier ever measured, producing the most icebergs of any Greenland glacier, and its behaviour has been a major focus of ice dynamics research since early systematic observations began in the nineteenth century.
The fjord into which Jakobshavn calves — Ilulissat Icefjord, a UNESCO World Heritage Site — is one of the most productive calving systems on Earth. Jakobshavn's icebergs are sufficiently large and numerous that they congest the fjord for most of the year, visible from satellite as a dense mosaic of white ice extending more than 50 kilometres from the calving front to the fjord mouth at Disko Bay. The iceberg density in the fjord is so great that the largest bergs, sometimes over a hundred metres in height, ground on the shallow sill at the fjord mouth and must wait for smaller pieces to drain before they can exit to the open sea.
Fjord Geometry and Ice Bed
Jakobshavn's fjord is exceptional in its depth. The main fjord channel reaches depths of over 1,000 metres below sea level for much of its length, making it one of the deepest fjords on Earth. This depth has a profound effect on glacier dynamics: the calving front at the terminus is a near-vertical cliff of ice hundreds of metres high, and the fjord provides a pathway for warm Atlantic Water — technically a subsurface Atlantic layer that underlies the colder surface waters of Disko Bay — to reach the glacier base. This ocean heat drives basal melting of the floating ice tongue and of the calving front itself.
The bedrock beneath the glacier, mapped using ice-penetrating radar surveys, extends far below sea level all the way to the main ice sheet interior. This retrograde slope — bed deepening toward the ice sheet interior — is the geometric signature of potential marine ice sheet instability, though the specific topographic configuration at Jakobshavn, including the narrow fjord width that constrains lateral spreading, complicates direct application of the classical instability mechanism.
History of Observations
Jakobshavn has been observed by Europeans since the colonial era, with early drawings of the icefjord by Danish sailors and naturalists in the eighteenth century. Scientific measurements of the glacier's front position began in the late nineteenth century through surveys by Danish Geological Survey teams and continued through the twentieth century with aerial photography, optical surveys, and eventually satellite imagery.
Through most of the twentieth century, the glacier terminus position was relatively stable, supported by a floating ice tongue that extended several kilometres into the fjord. The flow speed at the terminus was roughly 20 to 25 metres per day, already extraordinary compared to most glaciers. Then, starting around 1997 to 1998, the floating ice tongue began to break apart. By the early 2000s it had largely disappeared, and the calving front had retreated substantially and reorganised to a form where calving occurred at or very close to the grounding line rather than from the tip of a floating extension.
Acceleration and Retreat Since the 1990s
The loss of the floating ice tongue removed the back-stress that had been partially restraining the glacier's flow. Without this buttressing, Jakobshavn accelerated dramatically. By around 2004, its terminus speed had approximately doubled compared to the late twentieth-century baseline, reaching over 40 metres per day in some measurements — well over 14 kilometres per year at peak. The glacier also thinned rapidly, with the surface lowering by tens of metres in the first decade of the twenty-first century, a signal detectable from satellite altimeters.
The acceleration was not simply a case of removing a mechanical constraint. The warming of subsurface Atlantic Water entering Disko Bay and penetrating into Ilulissat Icefjord drove increased basal melting that thinned the floating ice tongue, destabilising it and triggering its fragmentation. The connection between ocean warming and outlet glacier dynamics at Jakobshavn became one of the best-documented examples of ice-ocean interaction in the world and helped establish the importance of this coupling — not just surface mass balance but also ocean heat — as a driver of Greenland mass loss.
A Partial Slowdown and What It Means
In an interesting development noted in research published around 2019 based on data from the mid-2010s, Jakobshavn's flow speed had decreased slightly and the terminus had thickened modestly compared to its early 2010s minimum. The cause identified was a cooling of the subsurface North Atlantic waters entering Disko Bay, associated with a shift in natural ocean variability — specifically the Atlantic Multidecadal Oscillation. The glacier had responded to reduced ocean heat by slowing slightly, demonstrating the bidirectional sensitivity of the system.
Glaciologists were careful to note that this short-term perturbation did not indicate a reversal of the long-term trend. The glacier remains far thinner, shorter, and faster than it was in the late twentieth century. The observation was valuable for confirming the ocean-glacier coupling — showing that the relationship between ocean temperature and outlet glacier behaviour is real and measurable — but should not be interpreted as a recovery.
Icebergs and Shipping Hazard
Jakobshavn's icebergs, many of them extremely large, drift south from Disko Bay through the Labrador Sea and some reach the Grand Banks of Newfoundland, where they have historically posed hazards to North Atlantic shipping. The most famous connection is indirect but real: the iceberg that sank RMS Titanic in April 1912 is widely believed to have originated from a Greenland calving glacier, most likely Jakobshavn or a neighbour, having calved the previous year and drifted south over many months.
The International Ice Patrol, established following the Titanic disaster, monitors iceberg positions in North Atlantic shipping lanes today, using satellite surveillance, ship observations, and aircraft patrols to track berg positions and issue navigational warnings.
Visiting Ilulissat
The town of Ilulissat is accessible by flight from Kangerlussuaq on Greenland's west coast, or by helicopter and small aircraft from Nuuk. The Ilulissat Icefjord UNESCO World Heritage Site is managed by the Greenlandic government, and visitor access to the fjord rim trails and overlook points is well-developed. The icefjord can be viewed from several designated walking trails and viewpoints, and boat tours from Ilulissat harbour navigate among icebergs in Disko Bay, providing close-up perspectives on the products of Jakobshavn's calving.
Use the map to locate Jakobshavn Glacier and Ilulissat Icefjord on Greenland's west coast and to explore the broader context of Greenland's outlet glacier network.