In Iceland, the valley of Skaelingar is dotted with rock pillars, considered as projectiles thrown into the moor by trolls warriors.
This mystery , interpretation satisfying the Icelandic and tourists eager to fantastic stories , has been debunked by two researchers from the University of Buffalo.
Valley of Skaelingar - Tracy Gregg Photo / Buffalo University
Basaltic pillars in the valley of Skaelingar - Photo Bramdamman.nl
These basaltic pillars , hollow , are indeed commonly found in the ocean a few kilometers below sea level , where when the lava meets the water under high pressure , it does not happen violent explosion ... but this is the first time that such formations are described on earth.
These basalt pillars form, in a deep sea, when hyper- heated water column come out on the ocean floor between the lava pillows and molten rock cools into hollow tubes shaped in minaret. These structures grow as the lava comes out and keep standing even after the eruption when the level of the lava fell . They were seen on the submarine ridge Juan de Fuca in the caldera of Axial seamount , interconnected at the top by a lava encrustée .
Axial seamount caldera - Submarine lava pillars connected by the top lava flow crust of the eruption of 1998, - NOAA Photo NEMO
Axial seamount caldera . - Collapse pillars in pit 98 - NOAA NeMo
These hollow cylinders , high for some almost two meters and a diameter less than the meter, have on their outer surface scars : these were formed by pieces of floating lava crust that have hit the pillars when the level of the washing decreased . The skin of the towers of basalt is not smooth , but knotted with bright drops . Glassy texture suggests rapid cooling and hardening of lava, at a pace that is compatible with non-explosive interactions between lava and water, as at mid-ocean ridges.
Skaelingar's valley - hollow basalt pillars - Tracy Gregg Photo / Buffalo University
To explain this unique phenomenon in subaerial environment, we must look to the place and the eruption that took place there : the Valley Skaelingar located at ~ 64.0 ° N , 18.5 ° W , which houses a tributary of the River Skaftá on one hand , and a basalt lava flow established during the eruption of Laki in 1783-1784 on the other.
Valley Skaelingar was temporarily filled by a lava flow, when the advance of large castings down the
Skaftá river was stopped , forcing the lava to flow into the adjacent valleys . After the dam in the valley of the
Skaftá river has jumped, debris were removed from the adjacent valleys .
The lava flows from the eruption of Laki, in brown
These subaerial pillars were formed at the slow progress of the lava flow ( of the order of centimeters per second) over a soil saturated with water , or temporarily flooded, forcing the water heated to interfere within lava lobes . They had a growth in height and diameter , as the lava flow is inflated. The pillars were left in place by removing of the flow . These structures thus reflect a non- explosive interaction between water and lava .
The search for such pillars of lava on land near the ocean will allow scientists to know the earlier sea level. Thanks to the discovery of such formations on other planets, such as Mars, we can determine where the water has been present in the past.
- Journal of volcanology and geothermal research - Non explosive lava-water interaction in Skaelingar, Iceland and the formation of subaerial lava pillars - by T.Gregg & K.Christle.
- University of Buffalo - News center - Water and lava, but - curiously - no explosion.
- Les éruptions de 1998 et 2011 à l'Axial seamount / Juan de Fuca ridge -