Читать книгу Hawaii Trails. Walks Strolls and Treks on the Big Island онлайн

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The Big Island is geologically an infant on an Earth more than four billion years old. Potassium-argon dating of rocks suggests that lava welled forth to build Kohala, the oldest of the island’s five or six volcanoes, beginning a little more than half a million years ago. Kohala is now extinct and is deeply eroded into spectacular valleys. Mauna Kea’s rocks overlie Kohala’s. Mauna Kea is old enough and high enough to bear the scars of glaciation during the height of the last ice age. Mauna Kea’s youngest-known lava flows are about 4,500 years old. Earthquakes still occur beneath Mauna Kea, so it’s considered dormant, not extinct. Hualalai volcano, on the west side of the Big Island, last erupted in 1800-1801 and is only dormant. Ke-Ahole Airport on the Kona coast is built on Hualalai lavas. Mauna Loa is still very active, having last erupted in 1984. Its lava came within four miles of Hilo on that occasion. Some scholars believe that an extinct volcano, Ninole, lies buried under the huge mass of Mauna Loa. On the east side of the island, Kilauea, the world’s most active volcano, continues an eruption that began in 1983. Written records of Kilauea’s eruptions reach back to 1824, but Hawaiian traditions assure us that it has been active ever since people first settled the Big Island. Only on Kohala can we say that erosion prevails, changing the landscape constantly. Elsewhere on the Big Island, volcanism may rework the landscape at any time.