Saturday, December 20, 2014
Needle Ice Creates a Vaulted Pebble Palace
Heavy rains followed by a hard frost December 7 made the garden path crunchy underfoot. A closer look revealed miniature pillars of ice with pebbles on top.
Water flows up from the soil via capillary action, with the upward motion continuing above ground as a column of ice fed from below. Needle ice is a surface form of the frost heaving that can loosen soil, slowly lift rocks towards the surface, and work mischief on asphalt.
The capillary action that allows water to move upwards in the soil is counterintuitive, and helps explain how trees completely surrounded by asphalt and concrete can still get water.