Lava coil

A lava coil is a spiral or scroll-shaped lava formation occurring when relatively low viscosity lava such as Pahoehoe solidifies along a slow-moving shear zone in the flow. The shear produces a Kelvin–Helmholtz instability that forms spiral-shaped patterns. Depending on the side of the flow the spiral is clockwise or anti-clockwise. They have been observed on flows near Kilauea on Hawai'i,^[1] in Kenya^[2] and possibly on Mars.^[3]

• Lava Coils on Earth and Mars
• 
  Surface of December 31, 1974 pahoehoe northeast of Pu‘u Koa ́e, Hawaii. Lava coil is 10 m diameter.
• 
  Spirals interpreted to be lava coils^[3] on the surface of a Martian lava lake in Cerberus Palus. Field of view is about 500 m.

References

1. " Dallas Peck, Lava coils of some recent historic flows, Hawaii. Geological Survey Research, B148-B151 1966
2. Temperley BN (1966) Vortex exudation coils on a recent basaltic lava in Kenya. Overseas Geol Mineral. Resour. 10:42--46
3. Ryan, A. J.; Christensen, P. R. (26 April 2012). "Coils and Polygonal Crust in the Athabasca Valles Region, Mars, as Evidence for a Volcanic History". Science. 336 (6080): 449–452. doi:10.1126/science.1219437.