July 31, 2003
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
The age of youngest volcanic rocks varies greatly among the Hawaiian Islands
It's an easy question to answer, "how old is the youngest volcanic rock on the Big Island?" With Kilauea in virtually continuous eruption, the youngest products are "right now!" But what of the other Hawaiian islands? The answer ranges widely, without a regular pattern for the age of complete extinction. On Maui, the youngest lava flows are those from Haleakala, emplaced either about 200 years ago (A.D. 1790) or 400 years ago (about A.D. 1600). This discrepancy, discussed in previous Volcano Watch articles, stems from the difference between oral tradition (the younger age) and radiocarbon ages (older).
West Maui volcano was last active about 0.38 million years ago, when the cinder cone Pu`u Laina erupted near Lahaina town. At about the same time, another cone, now largely quarried away, was active north of Ma`alaea. These eruptions occurred long after the main growth of West Maui, which ended about 1 million years ago. Sporadic eruptions occurring late in a volcano's history are commonly ascribed to a rejuvenated stage of eruptive activity. Kaho`olawe was last active about 1.15 million years ago. Nearby Lana`i probably ended its activity about 1.25 million years ago.
Moloka`i has two volcanoes. The younger, East Moloka`i, was largely finished by about 1.4 million years ago, but it experienced rejuvenated-stage volcanism more recently. Along its north shore, a small volcano built the Kalaupapa Peninsula between about 0.38 and 0.5 million years ago West Moloka`i volcano is not well dated. It probably last erupted about 1.8 million years ago.
O`ahu possesses surprisingly young rejuvenated-stage volcanic rocks. Eruptions as recently as about 50,000 years ago produced Koko Crater, one of the youngest of the features known as the Honolulu Volcanics. Diamond Head, another of the Honolulu Volcanics, is about 0.4-0.5 million years old.
On Kaua`i, the main volcanic episode ended about 4 million years ago. But sporadic rejuvenated-stage eruptions have persisted as recently as 0.5 million years ago. These lava flows were sampled on the east side of the island, whereas flows ranging from 1 to 2 million years are scattered more broadly. Source vents for specific lava flows aren't known, but the youngest Kaua`i flows may have issued from Kilohana Crater or Hanahanapuni.
Ni`ihau ended its shield-building stage about 4.9 million years ago. Latest eruptions may have been as recent as about 0.4 million years ago, the culmination of rejuvenated-stage volcanism that began 2.5 million years ago. The inception of island volcanism progresses down the island chain. Ancient Hawaiians had it correct in their story of the demigod Maui, who fished the islands from the sea. Last on his string was the Big Island, youngest of the islands to surface. The chants that record goddess Pele's flight down the island chain, reaching her current home at Kilauea, are also correct in describing the progression of shield-stage volcanism, the stage when over 95 percent of an oceanic volcano's lava flows are erupted
But when the shield growth ends, volcanoes dribble irregularly to oblivion. The duration of their waning probably depends on diverse and as yet incompletely understood phenomena. Are there differences within the lithosphere, the thick rind that includes the Earth's crust, that allow magma to reach the surface more easily beneath some volcanoes than others? Does the hot spot itself wax and wane so that more or less heat is available to drive the melting process? The answers to these as yet unanswered questions must explain the varying ages of youngest volcanic rocks from each island.
Eruptive activity at the Pu`u `O`o vent of the shield-building Kilauea Volcano continued unabated during the past week. Surface breakouts from the east-side lobe of the main Mother's Day flow extend down Pulama pali to just above Paliuli. Lava continues to move along the western edge of the Kohola flow from the top of Pulama pali to 750 meters (yards) beyond the base of Paliuli. The distal end of the active Kohola arm in the coastal flats is 1.1 km (.7 mi) from the end of the Chain of Craters road. Lava stopped entering the ocean at the Highcastle delta, and there is no ocean entry at this time.
There were no earthquakes reported felt on the island this past week.
Updated: August 5, 2003 (pnf)