Landbrotshólar

In Landbrot, right next to Kirkjubæjarklaustur, are Landbrotshólar, many clusters of pseudocraters, formed in the Eldgjá eruption in 934 to 940 when lava flowed over wetlands. Pseudocraters are formed when hot magma comes into direct contact with water-soaked substrates and causes the water to instantly boil. Magma flows through lava tubes, but where the magma bursts from the lava tubes, lava nuggets are formed. 

These lava nuggets bulge out due to magma flowing into them, but gradually the flow is limited to fixed lava pipes inside the semi-solidified lava. When the lava nuggets bulge out, their weight increases and the lava sinks into the substrate until the bottom crust breaks beneath the lava channel. This causes magma to flow directly into the water-soaked substrate, causing steam explosions that form pseudocraters on the surface. The explosive activity prevents further lava flows along the lava channel below the steam explosions, leading to a shift in the lava flow and the formation of new lava channels and new pseudocraters. This chain reaction goes on until the lava has worked its way over the wetland and built up a cluster of pseudocraters.

Very interesting, but easy, 9 km hiking trail is around Landbrotshólar and starts at the bridge over Skaftá. The route leads to Hæðargarðsvatn and from there to an old road between the pseudocraters.