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| Hole in Kalalau ridge at Keanapuka. Author photo, enlarged and color corrected by John Wehrheim |
The Hawaiian Islands are constantly eroding, and an example
of that erosion is a huge hole through one of the prominent ridges of Kalalau
Valley on Kaua`i—a window through a rock wall.
For most people viewing it, it looks like something brand
new, because they haven’t seen it in that location before. But perhaps it’s not
so new, and only being noticed now because it is only readily visible in
absolutely perfect lighting.
The nearly circular hole on the northeast wall of the valley
is a distinct feature visible near sunset this week from along the Pihea Trail,
which runs along the cliffs at the back Kalalau Valley.
It is only barely visible from the Pu`u O Kila Lookout, from
which the pierced ridge is viewed nearly end-on. Most of the popular photos of
the valley are taken from the lookout.
The hole is best viewed when the ridge
can be viewed from the side--a half mile or so from the lookout along Pihea Trail.
Was it always there, with the light just perfect in late
afternoon on November 5, 2017, so that it was suddenly visible?
Famed Isle photographer John Wehrheim said he has viewed the
same ridge from the same vantage point and from closer, and he never noticed
the big hole or puka. But the name of that part of the valley wall, Keanapuka, (cave open
at both ends) suggests there was at least some feature like it at that location.
“I’ve not seen it before and I’ve experienced this view many
times and from much closer vantages. But
that light is uniquely perfect for separating the puka from the ridge. My guess
is that the puka can only be seen clearly and obviously at this time of year with
its long low angle of light,” Wehrheim said.
His enlarged and color corrected version of my image is
shown ar the top of this story
So, a sheet of rock fell out of a narrow ridge, creating an
opening—at some point. But did it happen recently, or decades ago, or was it an
existing feature that got bigger?
Geologist Chuck Blay reviewed the images and said it may be
an unnoticed older feature in a particularly thin ridge on the Hawaiian
landscape.
“I can see why the hole in the ridge may have been there
without notice for some time. The
lighting seems to be just right for it to be noticeable at the time you saw
it. From its shape and location it
doesn't seem probable that it just all of a sudden developed,” Blay said.
The key to the visibility this week is that the near face of
the ridge is in late afternoon shadow, but the cliff face behind it is in full
sun, so the window-like brightness emphasizes the feature. Otherwise, the
greenery of the near side of the cliff would be indistinguishable from the
greenery immediately beyond it.
Also, the sunlight is at the perfect angle to illuminate the
rock that forms the inner wall of the puka. That helps put a pale gray border around the
hole and enhances its visibility.
These kinds of features—holes right through a rocky ridge—are
not uncommon in the islands. But they are also transient, as the islands’ lava cliffs,
piers and pillars erode from wind and water, and even from feral animal
traffic.
There is a feature on Kaua`i that was commonly called the
Hole in the Mountain, although it has mostly closed because of a collapse of
its roof. It was famous in Hawaiian legend as a hole pierced in the mountain by
a prodigious spear-throw from a Hawaiian hero.
Along the Na Pali Coast, there is a hole through a ridge
that separates the two beaches of Honopu Valley.
On the Big Island, there is the Holei Sea Arch in Hawai`i
Volcanoes National Park, and there was the Onomea Arch north of Hilo, which has
since collapsed.
On Molokai’s north shore, there is a walk-through cave
called Keanapuka just along Hakaaano. There are arches on Lana`i, Lehua, South and
East Kauai, and elsewhere in the Islands.
And there are lots more in these dynamic islands. Why does
the rock of the Islands erode so quickly? Geologist Blay has an answer.
“The shield volcanics in Hawaii are rather chemically
metastable owing that they were derived from the melting of upper mantle
material which is stable at high temperature and pressure but unstable at earth
surface temperature and pressure,” he said.
And in that is a caution. Hawaiian cliffs are notoriously crumbly and risky to walk under or climb on.
“The lava rocks of Kauai are mostly pretty rotten,” Blay
said.
“There is a good reason that sand size lava rock fragments
are rather uncommon in most of the beaches of the island. They fragment and dissolve before they get to
the coastal zone.
“We all know that rock climbing is not a good idea in areas like
Na Pali and Waimea Canyon,” he said.
© Jan TenBruggencate 2017
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