Geysir, sometimes known as The Great Geysir, is a geyser in south-western Iceland, that geological studies suggest started forming about 1150 CE. The English word geyser derives from Geysir. The name Geysir itself is derived from the Icelandic verb geysa. Geysir lies in the Haukadalur valley on the slopes of Laugarfjall lava dome, which is also the home to Strokkur geyser about 50 metres to the south.