Hawaii National Park by George Cornelius Ruhle

Author:George Cornelius Ruhle [Ruhle, George Cornelius]
Language: eng
Format: epub
ISBN: 9783337626556
Google: 4FPzugEACAAJ
Publisher: hansebooks
Published: 2018-08-25T00:40:49+00:00

GEOLOGY

THE ORIGIN OF THE SCENIC FEATURES

The Island of Maui was built by two volcanoes. That forming West Maui is deeply dissected into several high peaks. The old summit crater now is encompassed by the head of Iao Valley. Mt. Kukui, the highest point, has an elevation of 5,788 feet.

East Maui is built of three series of lava products from Haleakala Volcano whose flows extended westward across the present isthmus to come to rest against the base of West Maui Volcano. These represent three great periods of activity, the latter two being separated by a long interval of quiescence that was characterized by intense erosion and mild, if any, eruptions. Geologists designate these three periods by the names Honomanu, Kula, and Hana. The mountain was built over three rifts, northerly, easterly, and southwesterly, each extending about fifteen miles.

In earliest (Honomanu) time, about the beginning of the Ice Ages, a symmetrical shield like Mauna Loa was built of pahoehoe and aa basalts 8,500 feet above present sea-level. During the next (Kula) cycle, eruptions were more explosive in nature; flows were composed of more viscous andesite between which layers of ash and soil accumulated. Big cinder cones and extensive ash beds were formed at this time. Like Mauna Kea today, the Honomanu dome was capped by a craterless mound of cinders, 2,500 feet high, that was studded with many lesser cones. The summit was a mile east of the present top on Red Hill and a thousand feet higher than it is today.

As Kula eruptions declined and grew less frequent, running water cut deeply into the sides of the mountain and excavated four great valleys, Keanae, Kaupo, Kipahulu, and Waihoi, that had broad heads, thousands of feet deep. Numerous lesser valleys were later to be buried more or less by lava flows. Most of the eastern summit ridge was worn away; Kaupo and Keanae Valleys met near the summit and fused into a great depression like that near the head of Iao Valley today. At one time, a great flow of mud, probably triggered by an earthquake, swept all before it as it moved down Kaupo Valley into the sea. Its remnants today are 350 feet deep at Puu Maneoneo near the coastal road. A similar mass movement of rock on soft mud was started by an earthquake on April 2, 1868 at Wood Valley, west of the Kilauea Section of Hawaii National Park; the flow, in its precipitous descent, buried a village with 31 people and more than 500 head of stock.

In recent times, volcanism again quickened at Haleakala, giving the third (Hana) series of volcanics. This veneered the east and west slopes of the volcano, covered the floor of the depression, and pushed great lava flows through Koolau and Kaupo Gaps to the sea. Large flows and cones mask the divide that delimited the two great valleys. During Hana time, the northern rift alone remained inactive. The most recent activity, dated by Hawaiian legend as 1750, is represented by two bare, black flows above La Perouse Bay, the southwest corner of the island.

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