Almannagjá is a vast gorge, distinctive demonstration of a fault which marks the west part of a Þingvellir rift zone. It is one of a few places when one can easily walk inside a ridge zone normally hidden deep in worlds oceans. It is spreading with a constant rate of two centimeters per year. Unfortunatelly this movement is not smooth, it is rather done in big steps - earthquakes. Last tectonic activity was recorded in 2000. From time when Alþing was established in 930 the inside part of zone subsided to almost four meters.