geology – A Darker View

Solid Rock is Not Forever

Living with active volcanoes, one gets to see new landforms appear regularly. The landscape can get rearranged with little notice, with places I once visited buried under new rock. In my time living on Hawai’i, I have seen roads, bays and tide pools, and entire neighborhoods disappear under new lava. Watching new land created by these flows of liquid rock is mesmerising.

The 61G lava flow ocean entry at Kamokuna under the light of a full Moon

The opposite is also true around here, sometimes prominent landforms are erased by the actions of flowing water, or the incredible power of wind and wave.

Thus we bid farewell to the Hōlei Sea Arch, cast into the sea by the heavy surf generated by Hurricane Nolo.

The arch was one of the features of Hawaiʻi Volcanoes National Park found along Chain of Craters Road. Featured on park maps and served by a viewpoint and interpretive signs, thousands of tourists have stood atop the cliff to admire what waves had sculpted from the jagged black sea cliffs.

Those same waves have erased what they carved. Sometime around September 27th, the arch fell into the sea. Apparently, no one witnessed its fall, there are no Facebook posts or YouTube videos of falling rock. All we have are before and after photographs. This is understandable as the park was closed during the hurricane.

I last visited the arch over a year ago, travelling the park with my parents. It had been noticeably eroded by the waves, appearing much thinner around the base than on previous visits. It was only a matter of time.

Hōlei Sea Arch and the sea cliffs along the southeastern coast of Hawai'i — Hōlei Sea Arch and the sea cliffs along the southeastern coast of Hawai’i in 2025

Geology of Waikoloa

While writing up my visit to Goat House Tube I was again wondering how old the lava tube was, it is clearly old, but how old?

A Google Earth image of Waikoloa overlayed with a geologic unit map showing the various lava flows from Mauna Kea and Mauna Loa, pinks are Mauna Kea flows while Mauna Loa flows are green

Most of the Mauna Kea lava flows upon which Waikoloa sits are ten to twenty thousand years old, but the Mauna Loa flows that start just south of the village can be quite a bit younger.

Just a few miles south of the village one can find the 1859 Mauna Loa flow, the longest lava flow in the state representing a very long eruption that produced an enormous volume of lava. This is the flow that reshaped Kiholo bay, destroying the large fishponds that could once be found there.

A Changing Landscape

A tale of two lava lakes, of a landscape altered in way so dramatic it is hard to comprehend.

We think of solid rock being the ultimate in permanency, something about the world that should never change, at least in the span of a few months. Geologic change takes thousands of years, not less than one, it just seems wrong when this rule is violated.

Places we once stood, or parked a car, a hiking trail across a plain of solid rock… All gone in a dramatic upheaval. A parking lot the lies upon a block of rock the size of a supertanker, sitting hundreds of feet below where I once parked the car. Change is the reality of an active volcano.

The glow from a lava lake in Halemaʻumaʻu lights the clouds prior to the May 2018 eruptions

I have seen change on this scale once before when Mt. St. Helens removed a mountain top that stood upon the horizon of childhood memory. Here at Kilauea the change was a bit slower, but no less dramatic.

I look across that caldera and note the places that are the same, the places that are gone. I may understand what has happened and how, but still some parts of my mind insist that this just cannot be true… Solid rock should not disappear or crumble like a cookie.

The glowing pit of Halemaʻumaʻu with the new lava lake

The return of lava to the crater seems like a return of normalcy. There was lava here for years, there should be lava here. Perhaps the lava will cover over that yawning pit that should not be. Fill the yawning chasm that affronts my senses so.

Perhaps, if the crater continues to fill, flooded to the rim with new lava, a new caldera floor will form, the cycle complete. Perhaps it may be possible to once again walk across the floor of Kilauea Caldera.

The Volcanic History of Mauna Kea

The tour guides give the basic story behind the creation of Mauna Kea. The story given is simple… A hot spot in the mantle is the source for a plume of magma that punches through the oceanic crust and forms the Hawaiian volcanoes. As the pacific plate moves the islands are formed one by one, the latest being the Big Island of Hawaiʻi.

Puʻu Kole Panorama — A panarama from atop Puʻu Kole showing Mauna Kea and a distant snow covered Mauna Loa

This is basically correct, but is also a vast simplification of the process. If you want to learn more about the formation of these impressive volcanoes you need to look further.

Fortunately there is a good source for answers… The Geology and Petrology of Mauna Kea Volcano, Hawaii —A Study of Postsheild Volcanism, Edward Wolfe, William Wise, and G. Brent Dalrymple. This seems to be the definitive paper on the geology of Mauna Kea. Any time I see a list of references for the geology of the mountain, this paper appears. Published in 1997 it incorporates much of the earlier studies on Mauna Kea into one compendium.

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