Monday, October 24, 2016

The Hawai'i That Was: Rising Out of Depression on Kaua'i, and Sleeping Giants

There's a different part of Kaua'i, one that doesn't quite fit the image of dramatic high cliffs plunging into the sea. It's a lowland, a region of lesser hills and ridges that only rise a thousand feet or so, covered largely by rainforest. It's unusual because Kaua'i is often imagined as a single deeply eroded volcano that should have been evenly eroded from all directions. It turns out to be far more complicated than that. In fact, it can be thought of as two shield volcano complexes, one of which developed on top of another.
The head of the Sleeping Giant (and a tough short climb)
Nounou Ridge rises above Kapa'a and this lowland area called the Lihue Depression. The ridge is composed of the volcanic flows of the older shield, the Na Pali basalts, that date back to between four and five million years ago. Strangely, the basin below has younger rocks, the Koloa Volcanics, which date to between 2.65 million and 150,000 years ago. Why strange? If this basin were hollowed out by normal erosional processes, the rocks in the basin would be expected to be older.

The story involves the destruction of a portion of the original shield volcano that built up the island. Shields are huge volcanoes with gentle slopes, but they are inherently unstable. As has been noted in some previous posts in this series, huge avalanches sometimes cause portions of the volcano to slide into the sea. On Kaua'i, it appears that a large failure caused the eastern side of the island to subside several thousand feet. This formed the low depression, which was later covered by basalt flows of the Koloa Volcanics.

A decade ago, I climbed Nounou Ridge. A delightful trail climbs the flank of the mountain from a neighborhood above Kapa'a, offering some incredible views across the eastern part of the island.

Nounou Ridge is also called the "Sleeping Giant", and the ridge does indeed resemble a reclining big person. The story goes that a friendly giant help islanders with construction of heiaus and other structures. Celebrations followed, and the giant had too much to eat and grew drowsy and laid down for a nap. A very long nap (we've all been there, right?). I've seen stories that note that islanders started fires behind the ridge to highlight the profile in order to scare off potential invaders sailing in from offshore.

The mountain ridge in the distance in the picture above is Anahola Ridge, which like Nounou is composed of the older Na Pali basalts. If that steep pinnacle looks just a little bit familiar, think back to the memorable opening sequence of "Raiders of the Lost Ark".

The trail is mostly an easy climb to a picnic shelter on top of the "chest" of the giant. If you want to get to the high point, the "chin", you've got a bit of a climb ahead. The route (not exactly a trail anymore) is a scramble with a fair amount of exposure on both sides. I did the climb in ignorance (Read a field guide? Nah...), but I was glad to reach the summit. The view was outstanding.

The full extent of Anahola Ridge was visible off to the north, as well as the low country in between. The ridge is exposed to strong winds blowing off the ocean; note how the trees are bent over in the picture below.

The view to the south reveals Haupu Ridge, the memorable ridge that is viewed by most airplane passengers on the approach to Lihue Airport. The lowlands of the Lihue Depression fill the foreground, as well as the canyon of the Wailua River (Wailua Falls are hidden down there somewhere).

I would have included a shot of Waialeale, but as usual, the wettest mountain on Earth was shrouded in clouds.

"The Hawai'i That Was" is a series on the geology and anthropology of the Hawaiian Islands that explores the nature of the islands prior to colonization and the changes that have taken place since. If the rate of blog posting lately, well yes, it's been a busy time. Have patience, and we'll finish our trip around the island in no time!

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