 Aerial view toward the NE of the Pu`u Kapukapu fault scarp (maximum height about 320 m) in the Hilina fault system, south flank of Kilauea Volcano, Hawai`i. In Hawai`i, these tall cliffs are called "pali's". |
Fault
Faults are fractures or fracture zones in the Earth's crust along which one side moves with respect to the other. A fault scarp is a cliff or steep slope that sometimes forms along the fault at the surface. There are many types of faults (for example, strike-slip, normal, reverse, and thrust faults) ranging in size from a few tens of meters to hundreds of kilometers in dimension. |
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Mount St. Helens, Washington Scientists measure the distance between two benchmarks spanning the fault scarp of a thrust fault on the crater floor of Mount St. Helens. This scarp developed on the crater floor in 1981 as magma rose into the lava dome (backgound) before erupting onto its surface. The pressure exerted by the rising magma against rocks surounding the conduit caused the crater floor to fracture along a plane gently inclined toward the dome. Material above the fault (person kneeling on upper surface) was pushed over material below the fault (person in lower right); in this view the fault scarp advances toward the lower right; arrow indicates direction of movement. Scientists measured an increasing rate of movement of this thrust fault before two eruptions in June and October 1981, which helped them to predict both eruptions accurately. |
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Kilauea Volcano, Hawaii Scientist measures the vertical offset along a fault that moved as a consequence of a 7.2 magnitude earthquake on the south flank of Kilauea on November 29, 1975. The offset here is about 1.5 m; note fresh brown soil directly in front of the scientist. The total observed displacement along several similar faults of the Hilina fault system was at least 2.5 m (see image below for overview of the fault system). This earthquake resulted in dramatic ground movements along the south coast of Kilauea. |
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Hilina Fault System, Kilauea Volcano, Hawaii Aerial view to the north of the Hilina fault system, which consists of a series of normal faults with scarps as high as 500 m on Kilauea's south flank. The large-scale offsets and associated seismicity in the south flank are thought to result from gravitational instability of this part of the volcano and from the repeated injection of magma into Kilauea's east rift zone. In contrast, the northern flank of Kilauea is relatively stable because it is buttressed by the mass of Mauna Loa Volcano. |
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Hilton Creek fault, Long Valley Caldera, California Aerial view of a glacial moraine along McGee Creek that has been offset about 15 m by part of the Hilton Creek fault system. Note cars in parking lot (lower left) for scale. The Hilton Creek fault is much larger than suggested by this relatively small offset--its scarp in places is about 1,100 m tall and forms part of the eastern front of the Sierra Nevada. The northern part of the fault terminates in Long Valley caldera, about 5 km NNE from this site. |