> Much of the landscape is virtually impassable. It's the first time I've really ever seen such a vegetatively sparse landscape that was so inaccessible simply due to the terrain. In some areas, relatively "flat" landscapes were so rocky that I can't even imagine how one might traverse those.

There are certainly areas lacking in vegetation for natural reasons but much of the land is vegetatively sparse because the Vikings cut down all the trees:

> At the time of human settlement almost 1150 years ago, birch forest and woodland covered 25-40% of Iceland's land area

From: https://www.skogur.is/en/forestry/forestry-in-a-treeless-lan...