Jökulsárlón was created by the retreat of the glacier Breiðamerkurjökull. The Breiðamerkurjökull is a small glacier from the biggest glacier of Iceland, the Vatnajökull. When the glacier begins to retreat, the glacier melts at the lowest point. In the gulley where the ice used to be a glacial lake forms.
The Jökulsárlón flows into the ocean. The icebergs that break of the glacier, run aground on the bottom of the lake. When they melt enough, they float further towards the ocean. So at the point where the glacial lake flows into the ocean there are a lot of big icebergs. They only melt completely when they are in the ocean. The Jökulsárlón lake is one of the newest glacial lakes in Iceland. Around 1930 this glacial lake emerged after the retreat of the Breiðamerkurjökull. But since that time it's growing very fast. The lake is about 200 meters deep.
When we arrived at Jökulsárlón the second time we saw the Breiðamerkurjökull and the size of the glacial lake. At the parking area boat trips are offered across the glacial lake. There's also a souvenir shop and opportunity to buy coffee and waffles.
Near Jökulsárlón there are another two smaller, but lesser now glacial lakes.
The Breiðárlón and the Fjallsárlón, both glacial lakes are harder to reach by car, but just as beautiful. If you have the time, then drive up the gravel roads and visit the two less touristy glacial lakes.
Jökulsárlón is one of the bigger tourist attractions in Iceland