Landbrotshólar is the most extensive area of pseudocraters in Iceland, measuring about 50 km2. Pseudocraters form when lava flows into rivers or wetlands. When the 1100°C hot lava comes in contact with water, heavy explosions occur as the water boils instantly. This phenomenon is well known in Iceland, where the land is mostly characterized by lava, lakes, rivers and marshes. The age and origin of the lava of Landbrotshólar has been debated, but it is believed now to have originated from the volcanic eruption of Eldgjá in 934.