A very common sight in Iceland are moss-covered lava fields. These are massive expanses of lava draped with Woolly Fringe Moss. Due to the high porosity of the lava (vesicular basalt), rainwater quickly drains through the rock into the aquifers below. The surface of the lava fields are thus dry ecosystems. Woolly Fringe Moss is a pioneer species and usually begins to form when the lava is at least 100 years old. The moss is spongey and forms thick pillows on the lava. It is greyish when dry and immediately a verdant green when wet. The moss produces soil on the lava which can then support heathers and lichens.