Navigate Big Island Lava Fields: Read Pāhoehoe, ʻAʻā and Ahu Trail Markers

Big Island lava fields can look the same in every direction. There’s little shade and no soil to hold footprints, and the surface ranges from smooth, ropy rock to fields of sharp rubble. Many park routes across them are marked only by ahu, stacked-rock markers maintained by park staff. This guide teaches you to read the rock, follow ahu properly, and handle the moment you can’t see the next one.

Warnings

What You Need

Read it, pace it, follow it, stay found

1. 01

   Step 1: Tell pāhoehoe from ʻaʻā

   The two main Hawaiian lava types look and walk completely differently:

   • Pāhoehoe: a smooth, billowy, ropy or hummocky surface. It usually advances in small lobes and toes, so the surface is a jumble of humps and dips.
   • ʻAʻā: a rough, jagged, spiny surface of loose clinkers over a dense interior. It is slow, ankle-twisting, and cuts skin and boots.
   • In between are slabby and spiny pāhoehoe (broken, tilted plates and spiny crusts), which the National Park Service describes as transitional to ʻaʻā.

   A flow can start as pāhoehoe and turn into ʻaʻā farther from the vent, so the terrain can change under you mid-route.

2. 02

   Step 2: Watch for thin crusts and cracks

   Not all lava is solid underfoot:

   • Shelly pāhoehoe forms over gas blisters and open tubes, leaving thin crusts (“shells”) at the surface. USGS warns that hikers can break through a thin, overhanging crust or trip on a crack and fall on the abrasive, glassy surface.
   • The park warns that earth cracks, thin crusts and hidden lava tubes are common, and that sinkholes and unstable edges aren’t always visible, even in daylight.
   • Walk on the established route. If the surface sounds hollow or crunches like eggshell, step back onto the line you came in on.
3. 03

   Step 3: Double your time and set a turnaround

   USGS advises allowing twice the time you think a walk on hummocky pāhoehoe will take. A ranger’s “3 miles” can feel like 5 to 6 miles on smooth ground. Darkness also falls quickly this close to the equator.

   • Write down a turnaround time and stick to it, even if you haven’t reached your goal.
   • Start early to avoid midday heat. Lava fields are shadeless, and the park says daytime temperatures can reach the high 90s °F.
4. 04

   Step 4: Follow ahu the right way

   Ahu (stacked rocks) mark many routes across lava in Hawaiʻi Volcanoes National Park. They’re maintained by park staff, and in places like the East Rift Zone they may be the only thing keeping you on route.

   • Before leaving an ahu, find the next one. Only move on when you can see it.
   • If you can’t see the next ahu, stop. Look around slowly from where you are, then go back to the last ahu you were sure of. Don’t wander looking for it.
   • Look back now and then. The route looks different on the way out.
   • Never build, add to, move or knock down ahu. The park says stacking rocks can be culturally offensive, disorienting to other hikers, and potentially against the law.
5. 05

   Step 5: Plan for fog, rain and darkness

   The park notes that rock piles and cairns are hard to see in the dark. Fog and rain do the same. Sunny mornings are often followed by rain and wind later in the day.

   • If visibility drops and you lose the line of ahu, stay at the last one you can see until it clears.
   • If darkness catches you, the park advises staying put unless you know the trail very well and have a light.
6. 06

   Step 6: Keep backup navigation running

   • Before you go, study the route on a map: direction of travel, distance, and the major landmarks (cinder cones, the ocean, pali cliffs, the summit).
   • Take a compass bearing along the route at the start and note where the sun is.
   • Download offline maps, and consider recording a GPS track so you can retrace your path. Cell service is unreliable.
   • Check your position at every ahu, not only when you feel lost.
7. 07

   Step 7: Know the extra hazards

   • Volcanic gas: vog can cause breathing problems miles downwind. If there’s activity, stay upslope and upwind.
   • Unexploded ordnance: the park warns that WWII-era munitions may remain in the Kaʻū Desert and coastal areas west of Kaʻaha. Don’t touch it. Note the location and report it to rangers.
   • Closed areas are closed for a reason. Never enter them.
8. 08

   Step 8: If you’re lost: stop, stay, signal

   The park’s emergency advice: stay calm, assess before deciding, stay put (you’ll be found faster in one place) and stay warm. Make yourself visible: wave bright items in the open by day, use a flashing light at night, and use a whistle or mirror. Call 911 or Park Dispatch 808-985-6170 if you have signal. This is why you leave a trip plan with someone.

Tips

FAQ

Sources

• USGS: Eruptions of Hawaiian Volcanoes, Lava Flows (pāhoehoe and ʻaʻā)
• USGS HVO Volcano Watch: Pāhoehoe and ʻaʻā lava flows
• NPS: Lava Flow Forms (shelly, slabby, spiny pāhoehoe)
• USGS Fact Sheet 152-00: Viewing Lava Safely
• NPS Hawaiʻi Volcanoes: Hiking Tips (lava hiking, ahu in the dark, emergencies)
• NPS Hawaiʻi Volcanoes: Safety
• NPS Hawaiʻi Volcanoes: Leave No Trace (ahu)
• NPS Hawaiʻi Volcanoes: Maunaulu / Puʻuhuluhulu Day Hike (ahu-marked route)
• NPS: Rock Cairns