In earlier articles in this series we have considered the fact that our district stretches far inland, around the mid-level regions of Mauna Kea, across the saddle between that mountain’s summit and to the middle of the summit crater of its giant neighbor, Mauna Loa. We have also mentioned the narrow extension of Hamakua crossing some of the valleys on the windward coast of our Island’s northernmost volcano, Kohala, the subject of the most recent article. Thus, the lands of Hamakua stretch across portions of three of Hawai`i’s five volcanic mountains: Mauna Kea, Mauna Loa and Kohala.
The district of Hamakua is mostly laid across the slopes and summit of Mauna Kea. This massive volcano, which makes up 20% of the surface area of our Island, has lava flows that overlay some flows of Kohala volcano. For a while, both volcanoes were simultaneously active, so there was an interlayering of successive eruptions at their shared boundary areas. Mauna Kea is considered to be a “dying” volcano, in the last stages of its life. One indication of its age is the fact that the “shield,” the rounded and gently sloping upper portion so characteristic of middle-aged Hawaiian volcanoes and well revealed by Mauna Loa as seen from Hilo, has been capped by short-term explosive eruptions. These have buried the previous summit, with its presumed caldera, under layers of cinder, ash and fragmented rocks to create an irregular profile largely composed of pu`u, or cinder cones, hundreds of which dot the top and flanks of Mauna Kea. Some of these are quite large: a few are more than a mile across at their bases and several hundred feet high.
Mauna Kea is often said to be the tallest mountain on earth, a statement that usually requires elaboration on the distinction between “tallest” and “highest.” An easy way to clarify this is to point out that even a very tall person standing in swimming pool is usually not so high as a shorter person standing on the edge of that pool. Because Mauna Kea is the highest mountain in Hawai`i (and in the Pacific, for that matter), pushing up into the atmosphere about 13,800 feet; and because its base is on the ocean floor, roughly 18,000 feet deep, this Hawaiian mountain is clearly taller than the highest mountain on earth, Mt. Everest, by 31,800’ to 29,028’. Most of Mauna Kea is, of course, submerged in the waters of the Pacific Ocean. Recent geological models of the shape of Mauna Kea’s immense neighbor, Mauna Loa, suggest that it may claim the title of “tallest mountain” for itself – but more on that next time.
Possibly unique among Hawaiian volcanoes is Mauna Kea’s history of glaciation. Some 15,000 years ago Mauna Kea’s summit was covered by a cap of ice 28 square miles in extent, with a maximum thickness over 300 feet. The presence and the dimensions of the glacier are evidenced by abrasions on the rocky masses high on the mountain, by rocks that were ground up and scattered by the moving ice, and by moraines — deposits of these rocks left at the margins of the ice as it retreated at the end of the earth’s most recent ice age.
The streams formed by the melting ice cut drainage channels in the side of the mountain, including the drainage that feeds Kalopa gulch on the north-east side of the mountain, and those of Pohakuloa and Waikahalulu, which ran into the saddle area between Mauna Kea and Mauna Loa. Geologists are fond of streambeds and road cuts because they expose subsurface layers of the earth. In their study of these glaicial run-off channels they found evidence of three previous episodes of ice caps on Mauna Kea, starting about 70,000 ybp (years before the present). The earlier glaciers were larger because the mountain was higher then, and therefore colder. As Mauna Kea has subsided and ice has returned with global cooling spells, the summit’s lower elevation supported decreasingly extensive fields of ice. In an earlier article, we considered the qualities of the dense rock from lava erupted under the ice, for its superior edge-holding ability in ko`i, the Hawaiian adze.
Mauna Kea is certainly singular among Hawaiian volcanoes in having a lake near its summit. One of the highest lakes in the U.S. at 13,020 feet, Lake Waiau occupies the bottom of a cinder cone, Pu`u Waiau, on a bed of ash which may be underlain by permafrost, both of which keep it from seeping away into the ground. Its surface area is about an acre; when rainfall or snowmelt is heavy, it overflows down the Pohakuloa drainage. In periods of extended cold weather it is sometimes covered with ice.
Mauna Kea, like Kohala, had two distinguishable series of eruptions. The first is known as the Hamakua Volcanic Series. This ran from 375,000 to 270,000 ybp and was separated from the second, the Laupahoehoe Volcanic Series, by an ash layer. The ash is as much as five meters thick near Hilo but thins to about 2 ½ meters near Pa`auilo. The Laupahoehoe Series began about 188,000 ybp and has some lava as young as 4,500 years old, and ash only 3,600 years old. The oldest lava, as one would expect, is exposed in the lower sections of Hamkua’s sea cliffs. Relatively late in Mauna Kea’s eruptive history, a lava flow spilled over the pali of Hi`ilawe, where Ipu`u Falls has now cut down through it. The site called Napo`opo`o is on part of this lava, and the “Ti House” sits on a higher remainder of it.
The goddess of the snow, Poliahu, is the deity associated with Mauna Kea in the traditional culture of Hawai`i. Herb Kawainui Kane has beautifully rendered his vision of her, reclining in the form of the pu’u near the mountain’s summit that bears her name. One personal experience that bears on the presence of Poliahu came during a four day trek I took around Mauna Kea between 11,000 and 12,000 feet one December to commemorate my 50th birthday. On the last day of my circumambulation I found some large cardboard rubbish that had blown down from the mountaintop. Because it was too bulky for me to carry out and I didn’t want to leave opala on this beautiful mountain, I decided to burn it on the spot. As the flames and smoke rose into the cool mountain air, I felt a flush of unease and began to think that fire in the realm of Poliahu might be offensive, given the legends of conflict between Mauna Kea’s goddess and her fiery sister, Pele. As I pondered the most appropriate course of action, flakes of snow began to drift down out of a sky only lightly dotted with clouds. I let this manifestation guide my decision: I squelched the flames, compacted the remaining paper as best I could and left it for the sun and rain to dispose of. The snow stopped and I finished my trek late that afternoon in bright sunshine.
The science of geology and the power of the Hawaiian culture can intersect to present us with unforgettable experiences in Hawai`i, and this seems especially so here in the vast lands of Hamakua.
(Primary sources for the information summarized in this article are Volcanoes in the Sea, by Macdonald and Abbott, various contributions to Volcanism in Hawaii, Vol. 1, U.S. Geological Survey Professional Paper 1350, edited by Decker, Wright and Stauffer, Guidebook for Mauna Loa-Mauna Kea-Kohala Field Trip, Hawaii Symposium on How Volcanoes Work, by Porter, Garcia, Lockwood and Wise, and Roadside Geology of Hawai`i by Hazlett and Hyndman.)
Aloha a hui hou!