GEOSC 10: Unit 3: Plate Tectonics II Hawaii Volcanoes National Park, on the Big Island of Hawaii Here, we visit the great active caldera of Kilauea volcano

GEOSC 10: Unit 3: Plate Tectonics II

Hawaii Volcanoes National Park, on the Big Island of Hawaii

Here, we visit the great active caldera of Kilauea volcano. Then, in the next slide show, we walk to the glowing lava of Kilauea’s east rift, and see the earth turning inside out. All photos by R., C., J., or K. Alley, except two from the United States Geological Survey (USGS), and so labeled.


Dawn in the 2-mile-wide caldera of Kilauea. Shallow hot rocks produce steam from rainwater percolating through cracks.


Kilauea’s “Steaming Bluff” occurs where faults parallel to the 400-foot-high caldera wall intersect the surface, allowing steam to escape. (A caldera, by the way, is a big, complex crater.)

In the very-early-morning picture from March 11, 2007, above, the steam cooled and then sank into the caldera with a cool breeze. A little later in the morning, left, the steam was rising.


Ohi’a flowers


Steam rises along faults parallel to but back from the edge of the caldera, which is behind the camera. These faults were caused by the tendency of rocks to slump into the caldera.


Karen Alley films her father in Kilauea’s Southwest Rift. The layered rocks behind Dr. Alley (lava flows, plus pyroclastics--pieces thrown by the volcano) were split in 1971 to form the rift when rising magma inflated the surface like a balloon; an eruption then made the “lava fall” to Dr. Alley’s left.


Above, the Southwest Rift Zone of Kilauea as seen in March, 2007. Right, an aerial photograph, taken in March, 1985, showing the rift. The photo above was taken from the point marked by the tip of the arrow in the right-hand picture, looking in the direction of the arrow. The caldera of Kilauea is behind the camera in the picture above, and at the very top of the picture to the right.

http://hvo.wr.usgs.gov/gallery/kilauea/caldera/4303019_caption.html USGS photo by J.D. Griggs.


Left, a fern struggles to grow just below the toe of the 1971 lava flow of Kilauea’s Southwest Rift Zone. Above, the lush growth near the mouth of Thurston Lava Tube, on an older lava flow (about 400 years) on the eastern side of the caldera, shows that the lava will yield productive soils if given enough time.


Complex geology. The large rock labeled R above Dr. Alley was thrown by an earlier eruption, and lies in a layer of other pyroclastic pieces. Younger pyroclastic pieces slid off R, so those layers thin as they cross R. The lava flow, the youngest layer, cascaded into the southwest rift to Dr. Alley’s right, ending just above the yellow arrow.

R


Additional views of features in the previous slide, from the Southwest Rift of Kilauea, labeled in the same way to make them easier to recognize.

R

Later in the semester, you will get a chance to read rocks and tell history--CSI Geology. Here, for example, after some lava flows and big explosions, the large rock R was tossed in, then buried by additional things thrown by eruptions, then the rift opened in which Dr. Alley stood to take the pictures, and then a lava flow poured across the top and down into the rift, now ending near the yellow arrow.

If CSI Geology doesn’t make sense yet, don’t worry--it will later.



Volcanic gases include water and other chemicals, from rainwater circulating through rocks, but also from deep in the Earth’s mantle. The atmosphere and oceans formed from volcanic gases. A natural balance has existed for billions of years between the volcanic release of water, carbon dioxide, sulfur (the yellow in the picture above) and other chemicals, and the return of those materials to the deep Earth in subduction zones. Recently, human fossil-fuel burning has been releasing carbon dioxide about 100 times faster than volcanoes do. This is another topic we’ll look into later.


Halema’uma’u Crater, within the larger caldera of Kilauea, is now about one-half mile across and 300 feet deep. From 1905 to 1924, a huge lava lake occupied the crater, often barely 100 feet below the rim (the prominent line marked by the yellow arrow shows where the lava stood at one time). In 1924, the lake largely drained to feed an eruption of the East Rift Zone. Rocks fractured to let the lava out, also letting water in, which flashed to steam and on May 18 caused a very vigorous eruption for “quiet” Hawaii, throwing many-ton rocks as much as 1/2 mile (killing one person). The crater deepened to about 1500 feet, but by 1951 had filled to only half that, and filled further in eruptions of 1974. You don’t need to memorize these details, but we thought you’d find them interesting.


Landslides have fallen down the steep crater walls, often triggered by the shaking of the numerous earthquakes. Notice that muddy water drained out of the big landslide near the center of the photo, forming the light-colored deposit at the point of the red arrow.


Thurston lava tube. About 400 years ago, lava drained through this 10-30 foot high tube. A flow often hardens on the top and sides while remaining molten inside, and the tube drains when the eruption ends. Drips may harden on the ceiling as very strange “stalactites”. You’ll see some active lava tubes in the next slide show.


Left: Looking down into a tree mold. When lava hits a tree, water in the trunk boils, removing heat and solidifying a “shell” around the tree. The lava may then drain away, leaving the mold sticking up. In this one, a new tree has rooted in soil developed on the old flow, sending roots into the space left when the old tree burned away. The picture below, from the USGS, shows a tree mold a few hours after formation, with the lava still glowing and the tree fallen to the upper right.

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GEOSC 10: Unit 3: Plate Tectonics II Hawaii Volcanoes National Park, on the Big Island of Hawaii Here, we visit the great active caldera of Kilauea volcano