5 March 2020
A geological detour: the Geotimes pillow lavas at Wadi Jizzi in Oman
Earlier this week I made a brief trip to Oman as part of my (non-geological) day job, in this case attending the opening ceremony of Intaj Suhar, the Oman equivalent of the wonderful University of Sheffield Advanced Manufacturing Research Centre, which sits within my portfolio. On Sunday I took a detour inland to visit the famous Geotimes pillow lavas at Wadi Jizzi, about 30 km inland from the city of Sohar.
These rock are famous as they appeared on the front cover of the Geotimes Magazine in 1975 (the magazine is now known as Earth Magazine). I visited courtesy of a somewhat bemused taxi driver, who clearly could not really understand why I’d drive out into the desert to look at rocks. However, these are truly spectacular:-
Cutting across the outcrop are two well exposed altered basalt dikes:-
These altered dikes seem to be much more susceptible to weathering, so form distinctive gullies within the outcrop:-
These pillow lavas were formed within the Semail Ophiolite at the bottom of the Tethys Ocean. The William and Mary Blog has a nice explanation as to how they formed:-
“Pillows commonly form when lava is extruded under water. As lava disgorges from its vent on the sea floor it comes in contact with the surrounding seawater that rapidly quenches the lava to a glassy solid, thereby partially clogging the conduit and forcing to lava to ooze out nearby. This repetitive process of extrusion and rapid quenching produces the tube to pillow-like morphology.”
These pillow lavas are exceptionally well-preserved. The explanation for this might lie in the deposits on the other side of the valley:-
I suspect that these alluvial deposits might have covered the pillow lavas until recently, preserving them.
Pillow lavas are very hard, and the interlocking structure will give the rock mass considerable strength. As a consequence they are likely to be resistant to failure, and thus not a good place to go looking for landslides.