Key takeaways
- Harbor and grey seals inhabit Jökulsárlón lagoon, gathering in the cold water for abundant fish and shelter among drifting icebergs.
- Icebergs calve from Vatnajökull and drift across the lagoon for months before reaching Diamond Beach, shaped constantly by waves and sun.
- Ash streaks, dark bands and white ice reveal the glacier's layers of snow, volcanic ash and ancient compressed ice compressed over centuries.
- Arctic terns and other seabirds nest on Breiðamerkursandur, a dynamic sandbar shaped by waves, wind and the outflow from the glacier.
- Constant wave action flips, melts and fractures icebergs, stranding fragments of ice on the black beach in an endless cycle of transformation.
Seals of the Glacial Lagoon
Jökulsárlón's waters host two seal species: the harbour seal and the grey seal. Harbour seals, smaller and more abundant, haul out on the icebergs in groups to rest between feeding dives, their dark heads and spotted coats distinctive as they warm themselves in the rare Icelandic sun. Grey seals, larger and more solitary, tend to favour the quieter edges of the lagoon. Both species gather here because the glacier-fed waters bring rich feeding grounds. Fish congregate where fresh glacial meltwater meets the salt lagoon, and the seals follow their prey, using the drifting bergs as platforms for rest and observation. During this 3-hour tour, you'll observe these animals in their natural habitat, watching how they navigate between the ice chunks and dive for Arctic char and other fish species that thrive in these unique conditions.
The seals' presence changes with the seasons. Spring and early summer bring the most seals, as breeding populations move through the lagoon. Summer sees them hauled out more frequently as daylight extends, while autumn and winter bring quieter gatherings. The icebergs themselves serve as essential resting spots, allowing seals to escape the water's cold and to scan for predators. Your guide will explain the behaviours you witness and point out individual seals that often return to the same bergs, showing the site's importance to their annual cycle.
Seabirds Nesting on Breiðamerkursandur
The black sand peninsula of Breiðamerkursandur, visible from the lagoon's eastern shore, is a nesting ground for several seabird species. Arctic terns arrive in spring and establish colonies where they rear their young before the long autumn migration to Antarctic waters. Great skuas patrol the area, aggressive and territorial during breeding season, defending their nests with dive-bombing displays. You may also spot black-tailed godwits and other waders that exploit the lagoon's shallow margins and the nutrient-rich sands. The lagoon and its surroundings form an interconnected ecosystem where the birds depend on fish abundance and the stability of the ice and shoreline.
From the tour, you'll gain perspective on why this particular stretch of Iceland's south coast attracts such diverse bird life. The glacier, the lagoon, and the coastal plain create distinct ecological zones within just a few kilometres. The birds' presence is a visible sign of the lagoon's health and productivity. Your Super Jeep ride will bring you close enough to observe nesting behaviour and understand how seabirds and seals share the same waters, competing for fish yet maintaining distinct feeding strategies and times.
A harbour seal peers between towering blue icebergs
How Icebergs Calve from Vatnajökull
The icebergs floating in Jökulsárlón have travelled a short but dramatic journey from Vatnajökull, Europe's largest glacier. Calving occurs when the glacier's pressure and forward motion become too great for the ice to hold together. Massive chunks break away from the glacier's snout, tumbling into meltwater streams that carry them downslope into the lagoon. This process accelerates during warmer months when meltwater beneath the glacier lubricates its movement. The ice that calves today may be hundreds or thousands of years old, preserved in the glacier's layers and now released into the open water. The tour takes you onto the glacier itself via Super Jeep, allowing you to see the calving zone up close and understand the forces at work.
Once in the lagoon, icebergs begin a slow drift toward the sea. Ocean currents and wind push them toward the outlet, a journey that typically takes weeks or months. The bergs shrink as they float, melting from above and below. Some ground on the lagoon's bed and remain for years, slowly diminishing. Others reach the short river that connects the lagoon to the sea and are carried toward Diamond Beach, where waves finally break them apart. The size and shape of each berg depend on the ice it came from and the conditions it encounters.
Layers, Ash and Striped Ice
Look closely at Vatnajökull's ice and you'll see its history written in stripes and bands. Each layer represents a year of snowfall, compressed and transformed over centuries. The clearest layers are pure white or pale blue ice, formed from compacted snow. Between them lie darker bands, some created by wind-blown dust and rock particles that fell on the glacier's surface. Volcanic ash from Iceland's eruptions, including the catastrophic Laki eruption of 1783 and more recent events, stains the ice grey or black. Ash from the 1783 eruption, deposited in the upper glacier, is now visible in some of the icebergs you see today. This visual record allows scientists and visitors alike to read the glacier's age and the climate history locked within its structure.
During the ice cave tour, you'll enter tunnels where this layering becomes even more apparent. The walls reveal alternating bands of ice, and your guide will explain how to identify volcanic ash layers and understand what they tell us about historical eruptions and atmospheric conditions. The blue ice you see is compressed to such density that it absorbs red wavelengths of light and reflects blue back to your eye. This same ice, once locked in darkness deep within the glacier, is now exposed and will continue its journey through the lagoon before melting completely.
Ice Caves and Blue Ice Formations
The ice caves beneath Vatnajökull are among Iceland's most otherworldly landscapes. They form where meltwater streams flow through the glacier, carving tunnels and chambers year after year. The Super Jeep brings you to accessible cave entrances where you can step into a world of crystalline blue ice. The colour intensifies deeper inside the caves, where the ice is older and more compressed. Stalactites of frozen water hang from the ceiling, and the walls glisten with refrozen spray. Your guide will lead you safely through the passages, pointing out where water flows and explaining how these transient sculptures are constantly changing. In summer, new meltwater streams carve and enlarge the caves; in winter, freezing temperatures alter their structure.
The caves are not permanent features. They shift and evolve with the seasons, and access changes accordingly. This impermanence is part of their appeal and their challenge. The tour includes all necessary safety gear, and your guide's knowledge ensures you experience these caves responsibly. The blue light filtering through the ice, the echoing sound of water, and the palpable age of the ice surrounding you create an unforgettable encounter with the glacier.
Icebergs Flip and Reshape
An iceberg is never static. As it floats in the lagoon, its shape changes daily. Waves and currents erode the waterline, creating undercuts. The berg becomes unbalanced and suddenly flips, rotating to find a new equilibrium. A towering pinnacle may tumble into the water, sending up spray and creating waves felt across the lagoon. The berg continues to melt from all sides, developing caves and arches before they collapse. Striped and layered ice becomes visible as melting removes the surface. Some bergs fragment into smaller pieces, each one drifting independently toward the sea. This dynamic process means that no two visits to the lagoon will show identical ice formations.
Your guide will point out bergs at different stages of this transformation. You might see a recently calved chunk still sharp-edged and pristine, alongside older bergs riddled with melt pools and deformed by flipping. The constant motion and change are what make the lagoon visually dramatic and scientifically significant. The Jeep positioning allows you to observe this reshaping from multiple angles and understand how a single massive berg becomes the smaller, sculpted fragments you'll later see on Diamond Beach.
Journey to Diamond Beach
The icebergs' final destination is Diamond Beach, a black sand shore where the outlet river meets the sea. Waves carry smaller fragments toward the beach, grinding and polishing the ice until it becomes rounded and gem-like. These fragments, typically ranging from fist-sized to car-sized, accumulate on the black sand where they catch the light like diamonds, contrasting starkly with the dark shore. The sight is one of Iceland's most photographed scenes, a natural jewellery display that changes hourly with the tides and waves. Large icebergs occasionally ground on the beach and remain for days or weeks before the next big storm breaks them apart and carries them away.
The tour focuses on understanding the ice while it floats in the lagoon and within the glacier's caves, but knowing the ultimate destination of these bergs adds perspective to the experience. The journey from calving at Vatnajökull to grounding on Diamond Beach encompasses the entire life cycle of glacial ice released into the ocean. By the end of the 3-hour tour, you'll have witnessed where the bergs come from, explored the ice itself, and learned how they eventually reach the sea. This complete narrative transforms the lagoon from a mere landscape into a dynamic system where geology, hydrology, and time intersect.
