Hiking on the Big Island of Hawaii may require crossing lava flows for extended parts of a trek. On the west side of the Island the lava flowed in 1801 and 1859 so the trails are over rough rock that is less than 216 years old. The amount of weathering and erosion is minimal, except where the ocean has battered the shoreline.
We have been hiking each day across the lava flows and have encountered three surfaces. The most common lava we encountered was a’a, a basaltic lava of rough or rubbly surface composed of broken lava blocks called clinker. The loose, broken, and sharp, spiny surface of an ʻaʻā flow makes hiking difficult and slow.
We have also encountered pahoehoe which is more ropy, flowing, and undulating. The flow was more fluid and cooled slowly. The shape is more sculpted and varied. We have enjoyed crossing the hard surface. It is a bit like hiking across sandstone slickrock.
We have also found another surface, transformed by the ocean. Where the a’a has been battered by the ocean, the rough surfaces become worn down and the rocks become blocky and smoother. As we hike along, the boulders shift underfoot making progress slow.
A hike in the a’a is tiring and hot. The topical sun heats up the black boulders and since nothing grow in the lava desert, the whole area becomes very hot. Hiking in the morning is best and lots of water is recommended.
We are always looking for a route across the pahoehoe along the shoreline. A couple of our hikes have had long sections like this, prompting us to look for more.