scoria

The large cylindrical pukaos are made of red volcanic rock called scoria, while the Moai heads are carved from volcanic tuff.

The area shown here has distinctive landforms that include explosively-formed maar craters, lava domes built by viscous lava flows, and scoria or cinder cones formed around a single volcanic vent.

The researchers are convinced that these are true volcanic cones, similar to common volcanoes on Earth known as scoria cones and tuff cones.

Soon the deep green of durum wheat fields and shocking yellow of canola give way to rectangular lots of red scoria gravel studded with drilling rigs and horse head pumps.

Red scoria gravel drill pads are being laid down at a rate of 200 a month.