This site marks the end point of the great Þjórsárhraun, the greatest lava flow on Earth since the end of the last Ice Age. The Holocene lava field on which you are standing was created by an enormous eruption around 6700 B.C., which originated in the Heljargja canyon in the Veiðivötn, the volcanic crater lakes near Landmannalauga.
The great Þjórsárhraun
The lava flowed for at least 140 kilometers before it finally stopped here, and its flow remains visible in the skerries (small rocky islands) that you see off the coast at Stokkseyrie. This one of the few places where the lava field is sitll visible, as it is covered by a thick layer of soil elsewhere. Another place where you can see the lava flow is at the nearby Urriðafoss waterfall.
The lava flow at Urriðafoss
The lava that created this site is known as 'pahoehoe lava', which is basaltic lava that has a smooth, billowy, undulating, or ropy surface. These surface features are due to the movement of very fluid lava under a congealing surface crust. Pahoehoe lavas typically have a temperature of 1100 to 1200 °C, and pahoehoe flows occasionally form lava tubes where the minimal heat loss maintains low viscosity, allowing it to flow more smoothly. You can see an example of lava tubes at the nearby Raufarholshellir Earthcache. The surface texture of pāhoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture. The rounded texture makes pāhoehoe a poor radar reflector, and is difficult to see from an orbiting satellite (dark on a Magellan picture).
Pahoehoe Lava
To complete this Earthcache, please answer the following questions by email (do not post them in your log):
1. Walk across the dune to the beach. What evidence do you see that the skerries (rocky islands) are the result of a pahoehoe lava stream?
2. The lava flowed approximately 1km into the sea, but much less is visible. Do you think the lava flow that is hidden under water looks the same as the skerries that you see? Why, or why not?
3. Why did the lava suddenly stop here?
4. Upload a photo of yourself or your GPS at the site. (Optional)
You do not need to wait for permission to log this Earthcache, but you must email us your answers within 24 hours of logging. If no answers are received or if the answers are incorrect, we will contact you and remove your log.