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Fire vs. Water: Erosional/Depositional Geology, Hawaiian Islands |
| Even a casual, untrained observer will see evidence that opposing forces have formed the Hawaiian Islands. The massive and lofty volcanoes have been scoured, abraded, and lacerated by streams and the sea. On the oldest islands (in the northwest) the volcanic mountains have been eroded and deeply cut by canyons. Even farther north are coral reefs and atolls--all that remain of former islands. This slide set examines volcanic features and their erosion by waves, glaciers, streams, and storms. The images include dramatic examples of Hawaii's unique geology. |
Mauna Kea, Hawaii. Evidence of glaciation during the last ice age. | |
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Mauna Kea, Hawaii. Evidence of glaciation during the last ice age. Here at the very summit of Hawaii, the evidence of the fire and water conflict is visible. During the last great ice age (ending 15,000 years ago), the summit of Mauna Kea was covered by a small glacier that left smooth, pale-gray deposits. These deposits are broken by cinder cones, indicating that volcanism was occurring at the same time. Photo credit: John Lockridge |
Haleakala, Maui. Caldera erosion. | |
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Haleakala, Maui. Caldera erosion. Haleakala is not as high as Mauna Kea and Mauna Loa on the Big Island (Hawaii) but it is older and its roots extend deep below the ocean floor. Today, Haleakala is the meeting place of four huge valleys-canyons that have been eroded in the weaker rock of the original caldera. These valleys, like many in the Hawaiian Islands, are shaped like huge amphitheaters. An amphitheater results when the upper portion of a valley grows more rapidly that the lower portion. Rejuvenated volcanism has partially filled the stream-carved canyons with ash, lava, and cinder. Cinder cones dot the floor of the summit basin. Haleakala is now 225 km (140 mi) northwest of the hot spot and is in the rejuvenated stage of volcanism. It last erupted about 200 years ago. Photo credit: Carol Gerlitz, National Geophysical Data Center |
'Iao Needle, Maui. Caldera erosion. | |
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'Iao Needle, Maui. Caldera erosion. The feature that looks like a pinnacle is a portion of a steep winding ridge that divides two valleys. The feature is a remnant of west Maui's caldera. The rocks in 'Iao Needle are thin, Wailuku basalt flows with many dikes cutting through them. Rising magma drove hot water, steam, and other volcanic gases through the porous rubble and lava in the floor of the caldera. One of the reactions transformed the mineral pyroxene into the green mineral chlorite, making the basalt green. The altered rocks in the old caldera weather and erode easily. This explains why 'Iao Valley opens upstream into such a broad basin. Photo credit: Carol Gerlitz, National Geophysical Data Center |
Na Pali Coast, Kauai. Site of a huge landslide. | |
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Na Pali Coast, Kauai. Site of a huge landslide. These steep cliffs are nearly 823 m (2,700 ft) high. A huge landslide may have taken place in this area several million years ago. Rubble from a giant slide is visible for miles on the ocean floor, northwest of Kauai. After the slide, the landslide scar was cut by stream erosion, and submerged in submarine canyons. The cliffs seen here are now well inland from the original, giant slide. Rock falls, chemical weathering, and erosion from small streams continue to sculpt this dramatic area. Photo credit: John Lockridge |
Kalalau Overlook, Kauai. Combination of landslide and water erosion. | |
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Kalalau Overlook, Kauai. Combination of landslide and water erosion. View of the Kalalau Valley, and the ocean 1219 m (4,000 ft) below. The horizontal lines in the cliffs are thin flows of Na Pali Basalt that poured down the north flank of the then-still-growing volcano on north Kauai. As the volcanism continued to add weight to the surface of the volcanic pile, weakened rock below the surface collapsed, taking a section of the island into the sea. On these steep cliff faces, warm acidic rainwater dissolves shady areas and evaporates on sunny, windy surfaces. Deep gullies form in the shady areas while ridges are left in sunny areas, creating a fluted pattern on the cliffs. Photo credit: William A. Braddock, University of Colorado |
Waimea Canyon, Kauai. Stream erosion of a normal-fault graben. | |
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Waimea Canyon, Kauai. Stream erosion of a normal-fault graben. This canyon, 22.5 km (14 mi) long and often 762 m (2,500 ft) deep, exposes much of the interior structure of what was once the volcano that built Kauai. Waimea Canyon follows the western edge of the Makaweli graben. This is a trough that dropped between two faults, and then was partially filled with lava when the volcano resumed its activity. The ancient fault scarps provided the foundation for the erosional features that make up the modern landscape. Streams have transported sediment from the area to give the land its rugged appearance. Red, weathered rocks, lush green vegetation, an abundance of waterfalls, and strange rock formations make this one of the most scenic spots on the islands. Photo credit: Carol Gerlitz, National Geophysical Data Center |
Waipi'o Valley, Hawaii. Eroded and partially-filled stream valley. | |
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Waipi'o Valley, Hawaii. Eroded and partially-filled stream valley. The northern section of the Big Island (Hawaii) was formed by Kohala Volcano. The resistant cliff walls were cut by a deep canyon that today is known as Waipi'o Valley. The valley, carved by stream erosion, was once much deeper than at present. It was filled with water when the sea level rose at the end of the most recent ice age. Streams and landslides poured mud, sand, and gravel from the weathered lava cliffs into the submerged part of the valley, partially filling it and creating the flat valley floor. When the sea retreated, the early Hawaiians cultivated this fertile valley floor. The little flat area at the base of the sea cliff (extreme right in photo) is the debris from a large rockfall that occurred at the time of the April 3, 1868, earthquake. Occasional rockfalls and relentless waves keep the sea cliffs steep. Because of its shape and location on the north coast of the Big Island, Waipi'o Valley is especially vulnerable to tsunamis. The April 1, 1946, tsunami crested at 12.2 m (40 ft) at this location, and inundated the valley 805 m (half a mile) inland. Photo credit: John Lockridge |
Wailua Falls, Kauai. Stream erosion; resistant layers overlie less resistant pillow lava. | |
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Wailua Falls, Kauai. Stream erosion; resistant layers overlie less resistant pillow lava. A thick flow of basalt lava confined by existing valley walls poured into a pool or swamp on the floor of the ancient Wailua River Valley. Pillow lava formed as the lower portion of the lava flow, 3 to 9 meters (10 to 30 feet) thick, entered the water. The ordinary pahoehoe lava in the upper part of the flow is much more resistant to erosion. The rocks near the bottom one-third of the falls erode quickly, undermining the more resistant lava layers on top. Occasionally, slabs break off the undercut lava, keeping the lip of the falls sharp. Flooding which follows winter storms washes away the debris. This double cascade on the south fork of the Wailua River is about 24.4 m (80 ft) high. Photo credit: John Lockridge |
Hawaii Volcanoes National Park, Hawaii. Erosion by plant roots begins on a new flow. | |
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Hawaii Volcanoes National Park, Hawaii. Erosion by plant roots begins on a new flow. Ground cracks abound in rift zones along the flank of Kilauea. These cracks expand and contract as lava enters and leaves the magma reservoir near the summit caldera. Acid steam, an effective erosion agent, escapes from many of these cracks. The cracking, together with the work of ground water, breaks up the flow so that plant roots can take hold. Cyano bacteria are the first organisms to live on a new lava flow. Lichens come next. Grass and moss work to turn the lava into soil. These soil-making forces work faster on the wet, windward sides of the islands than on the dry, leeward sides. Chemical reactions between water and the silicate minerals in the basalt produce clay of various types. Photo credit: John Lockridge |
Hanakapiai Beach, Na Pali Coast, Kauai. Stream erosion meets wave erosion. | |
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Hanakapiai Beach, Na Pali Coast, Kauai. Stream erosion meets wave erosion. Boulders rounded by abrasion (from storms) lie at the mouth of this small stream on the Kalalau Trail. Stream erosion is one of the most important denudational processes. The royal blue waters tumble past these boulders to reach the azure blue waters of the ocean. This azure blue color is visible only in shallow water beyond the coral reefs and only when the sun shines. The phenomenon occurs when the sun reflects on sediment suspended in the water. Deeper water appears darker since less light reflects off the bottom, and the waves do not stir up sediment. The light, the depth of the water, and the amount of suspended sediment determine the color of the water. In addition, in places along Hawaii's shores, the nature of the bottom is a factor. In shallow water the sand-covered sea floor gives a blue-green tint while reef or rock creates a darker blue appearance. Photo credit: John Lockridge |
Pepe'ekeo Scenic Drive, Hawaii. Eroded headland north of Hilo. | |
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Pepe'ekeo Scenic Drive, Hawaii. Eroded headland north of Hilo. This headland is evolving into a sea stack or island. Waves tend to refract toward headlands, concentrating their energy as they attack from both sides. Compressed air, forced by the waves into fractures in the rock, widens the fractures and forces blocks of rock into the sea. Photo credit: John Lockridge |
Puna Coast, Hawaii Volcanoes National Park, Hawaii. Relentless waves erode sea cliffs. | |
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Puna Coast, Hawaii Volcanoes National Park, Hawaii. Relentless waves erode sea cliffs. When the hot lava poured into the sea at this location, the lava was pulverized into sand and the advancing flow overtopped this material. Periodically the flow front collapses, leaving a cliff. In this photo, high waves pound the 15.2 m (50 ft) high cliffs. Note the slack rock protruding from the waves-a cliff remnant showing how the sea has reduced the extent of the land at this location. (For scale, note the white automobile on the top of the cliff, and trees on the cliff in the background.) Photo credit: John Lockridge |
Puna Coast, Hawaii Volcanoes National Park, Hawaii. Sea arches. | |
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Puna Coast, Hawaii Volcanoes National Park, Hawaii. Sea arches. Here, where the lava flows from Kilauea enter the sea, waves have carved a sea cliff, and have taken advantage of weak zones of fracturing or rubbly rock to create this sea arch. Photo credit: John Lockridge |
Kahakuloa Head, Maui. Wave-sheared headlands. | |
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Kahakuloa Head, Maui. Wave-sheared headlands. The windward coast of West Maui receives the full brunt of the trade winds and North Pacific gales. The result is a cliff-lined shoreline with headlands such as these sheared by wave action. Pu'u Koa'e, the eroded volcanic dome at the left in the slide, is located on the east side of Kahakuloa Bay. Photo credit: Carol Gerlitz, National Geophysical Data Center |
Holei Pali, Hawaii. Slump scarp draped with lava flows. | |
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Holei Pali, Hawaii. Slump scarp draped with lava flows. As Chain of Craters Road winds down the side of Kilauea toward the sea it crosses this pali (cliff). The pali is actually a slump scarp about 427 m (1,400 ft) high where the south flank of Kilauea is slumping into the sea. Pahoehoe (smooth ropey lava) and a'a' (rough clinkery lava) have spilled over the cliff and are both visible in the picture. The area below this cliff has dropped down relative to its former position. Photo credit: John Lockridge |
Kona Coast Beach, Hawaii. Marine erosion; white coral pieces deposited by storms. | |
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Kona Coast Beach, Hawaii. Marine erosion; white coral pieces deposited by storms. Large blocks of white coral form a sharp contrast to the black basalt flows on this storm beach. The chunks of coral, deposited by storms, lie beyond the normal reach of high tide. Chunks of this coral are used as "natural" graffiti to decorate the black lava flows along Highway 19 on the Kona coast. In winter, storms strip sand from these beaches, revealing jagged rocks. Photo credit: John Lockridge |
Kaihalulu Beach (Red Sand Beach), Maui. Marine erosion; sand from cinder. | |
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Kaihalulu Beach (Red Sand Beach), Maui. Marine erosion; sand from cinder. The name Kaihalulu means "roaring sea." This beach cove is located on the seaward side of Ka'uiki Head, a large cinder cone near the town of Hana. It originates from the marine erosion of the cinder. Oxidized iron compounds give the cinders and the sand the red color. Note the black basalt protruding from the bay at the right. This is part of a lava breakwater that extends across the bay, protecting the beach from the waves of the ocean. Photo credit: Carol Gerlitz, National Geophysical Data Center |
Papakolea Beach (Green Sand Beach), Hawaii. Marine erosion; olivine in the sand. | |
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Papakolea Beach (Green Sand Beach), Hawaii. Marine erosion; olivine in the sand. This secluded sand beach is located near South Point in the Kau district of Hawaii. The erosive force of the ocean washing into the base of Pu'u o Mahana, a littoral cone, has extracted olivines (small green mineral grains) out of the cinder. These are deposited on the sand, giving the sand a green tint. Photo credit: Carol Gerlitz, National Geophysical Data Center |
Wai'anapanapa Black Sand Beach, Maui. Marine erosion; bits of basalt. | |
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Wai'anapanapa Black Sand Beach, Maui. Marine erosion; bits of basalt. The dark-colored sand on this beach comes from wave erosion of basalt in the sea cliffs surrounding the beach. This dark gray, dull sand is not at all like the black, glassy sand found on beaches on the Big Island (Hawaii). Glassy black sand is formed when molten lava enters the ocean; steam explosions blast the liquid rock into fine pieces of volcanic glass. In either case, waves and currents sweep the sand into sheltered coves where it collects to form the "black sand beaches." Photo credit: John Lockridge |
Spouting Horn, Kauai. Marine erosion; lava tube turned water tunnel. | |
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Spouting Horn, Kauai. Marine erosion; lava tube turned water tunnel. Waves rush into the mouth of a lava tube that is open to the sea, making the sound of a horn. Periodically, a fountain of water shoots up through a hole in the roof of the tube. Waves sculpted this flat bench in the lava when sea level was about 1.5 meters (five feet) higher than now. This bench now provides the stage upon which the fountains perform. Waves will eventually erode the platform. Photo credit: John Lockridge |