The Saturday after Thanksgiving I went on a hike with several co-workers to a location on Hawaiʻi known as the Great Crack. The Great Crack is, well, a giant crack on the south-west flank of Kīlauea. In fact, it roughly coincides with Kīlauea's comparatively laid-back south-west rift zone. For context, each Hawaiian volcano has two or three rift zones along which most of their activity is concentrated during their pre-shield and shield phases (along with their summit craters). For example, Mauna Loa has an east rift zone and a south-west rift zone, and its two main arms coincide with those zones. Kīlauea is similar, in that it has an east and a south-west rift zone. In Kīlauea's case, the east zone has historically been much more active. In the years since historically reliable reports of Kīlauea's eruptive activity began around 1820, the south-west rift zone has experienced just five events, compared to twenty-nine for the eastern rift zone.
Anyway, the Great Crack coincides with the south-west rift zone and stretches for a distance of seventeen miles down the flank of Kīlauea just outside Volcanoes National Park. It apparently had an eruptive event in 1974 (though I haven't been able to find just what was involved), and another in 1928 where lava seeped from the lower half of it. It's not exactly set up as a tourist attraction, unlike places such as Kīlauea caldera. There are no easy trails to it; it lies a few miles – at closest – to the island-encircling Māmalahoe highway. According to the GPS tracking app I used we hiked for almost three miles over rough-and-tumble terrain to get to it.
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| The vast bulk of Mauna Loa rises to its lofty head, lost in clouds. |
This is the kind of terrain we were hiking over, short scrubby grass and trees intermixed with several-hundred-year-old lava flows. This is looking backwards towards Mauna Loa, however, which was behind as we hiked in. I'm honestly amazed we didn't get lost following the trail, as it was in many places not at all obvious that it actually
was a trail.
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| Lovely rippled pāhoehoe. |
Some of the nifty lava formations we were hiking over. You can tell this is old lava because of its brown color and weathered look (fresh lava is much more black).
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| Approaching the crack, “Mordor” began to be the comparison my mind made. |
And for comparison, this is lava from 1928 (most likely). We ran into it extending perhaps a quarter mile from the crack all along its length (at least the part we hiked, which was near the middle). You can see how much darker it is.
The crack turned out to be widely variable in width along its length. Periodically it would close up entirely allowing us to walk from side to side, while in other places it was easily over a hundred feet wide. The wide sections all had lots of rubble on the floor that had obviously sheared off from the walls collapsing. This fact was not lost on us as we tried to approach the edge to look in! I kept feeling as I was walking that there were hollow pockets in the ground beneath my feet, which was unnerving, and promoted a great desire to walk softly and quietly. All that notwithstanding, I was still able to get some nice shots of some of the wide areas from further along where the crack closed up again.
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| Great Crack indeed. |
Here's looking towards one section where it closed up from further along.
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| Another part of the crack. |
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| Looking down along the crack. |
It's a bit hard to see in this photo, but from this vantage point we could follow the path of the crack as it meandered down the slope till it disappeared in the distance over the cliffs. It's also hard to see, but there's a fence on the left side of the crack running roughly parallel with it which is the boundary of Volcanoes National Park.
The inner wall of the crack, in the places where it hadn't sheared off, looked very similar to what you might find in a lava tube.
We also saw a lot of lava tree casts along the way, which was pretty neat. The lava kind of piles up around the trees and hardens before the tree burns away, leaving this large lumps of solidified lava with holes in them. Sometimes the lava has a strangely rope-y or braided look to it, such as the one below:
Another thing I noticed as we went along were small, oddly shaped rocks that stuck out from their surroundings. As far as I can tell they were splatters of lava forcibly ejected from the crack at some point that held together through surface tension and hardened when they hit the ground. I got a picture of one at random, as they were scattered pretty liberally around the crack.
After the three-mile hike to the crack over rough terrain we didn't feel like too much more hiking over pāhoehoe, so after walking a bit down the crack (and coming to the overlook I tried to photograph) we turned back. The entire hike was about six and a half miles, though the vertical change was no more than a few hundred feet. I definitely wasn't expecting the three-mile hike through scrubby bushes and grass at the beginning, I thought it would be lava or mostly lava the entire way. Thankfully the weather was about as good as we could have hoped for, overcast and cloudy with a strong breeze from the south nearly the entire time keeping the vog away. All in all it was a fun hike. It's definitely not a casual hike with the trek in, but it's a great view when you get there.
