Grabrok crater rises about 170 meters above the ground and is easily accessible via a footpath. It’s quite steep, so steps have been built on part of it to make the hike easier.
Grabrok belongs to the volcanic system of Ljosufjoll. It reaches from Berserkjahraun in the North of the Snaefellsnes peninsula, close to Stykkishólmur, over the actual Ljósufjöll and Hnappadalur all the way to the Grabrok craters. It extends over a distance of 90 km and is one of the longest in Iceland. The last eruption took place about thousand years ago at Hnappadalur.
The crater is the largest of three and was formed about 3400 years ago in a fissure eruption. The lava that now forms the lava field Grabrokarhraun came from these three craters; Stora Grabrok, Grabrokarfell and Litla Grabrok. The lava blocked the path of the Nordura River and pushed it further east. It also blocked the hollow where Hredavatn lake is today, forming the lake. Beautiful water streams come up from the lava in several places, the biggest ones are in Paradise Hollow.
A brisk walk from the parking lot to the top of the crater and back again takes about 40 minutes. Once at the top you have an incredible view of the Borgarfjordur country-side and the encircling mountains.