A lagoon born from retreat around 1935
What you see today started when a lagoon formed at the glacier edge around 1935. As Breiðamerkurjökull kept retreating and the lagoon expanded rapidly around 1950, the place stopped behaving like a fixed landmark and began feeling like a live geological process.
Why the black sand fills with ice
The short glacial river linking the lagoon to the Atlantic keeps moving ice between calm water and surf. That is why Fellsfjara, the shore most travelers call Diamond Beach, can look sparse one hour and glittering the next.
Seals and birds change the rhythm
For all the glacier scale, the stop is not only about grand scenery. Seal colonies gather where the rivers meet the sea, and the wider Breiðamerkursandur area matters for nesting birdlife, so quiet watching can become just as memorable as the postcard view.
The short Helguhóll climb explains the whole layout
From water level, the lagoon can feel like separate viewpoints with no clear logic. The easy Helguhóll loop fixes that: once you are slightly above the shore, the glacier tongue, the lagoon basin, the river, and the black-sand plain suddenly read as one connected landscape.