November 15, 1996
A weekly feature provided by scientists at the Hawaiian Volcano
Observatory.
Kilauea has its faults
Visitors to the lava viewing area at the end of the Chain of Craters
road in Hawai`i Volcanoes National Park travel over one of the largest
fault systems on the island on Hawai`i. The Hilina fault system,
located within the south flank of Kilauea Volcano, consists of a series
of subparallel and en echelon normal faults.
Normal faults are fractures in the Earth's surface where one block
appears to be displaced downward relative to an adjacent block. They
occur in areas subject to tensional stress or extension.
The gravitationally induced seaward sliding of the unbuttressed
south flank of Kilauea Volcano produces the tensional conditions.
Periodic measurements by the U.S. Geological Survey's Hawaiian Volcano
Observatory (HVO) indicate that the coastal areas are moving at a rate
of 2.5 inches per year, about as fast as your fingernails grow, while
inland areas are moving at slower rates.
Occasionally, the entire flank will move rapidly and far, as it did
during the early morning hours of November 29, 1975, when a
magnitude-7.2 earthquake occurred. Parts of the Hilina fault system
were displaced over 10 feet seaward and another 10 feet downward during
the earthquake. The dynamic nature of the region makes it a natural
laboratory for surface deformation studies.
Through cooperative investigations with the University of Hawai`i
and Stanford University, HVO receives data from a network of 13
continuously recording GPS stations located from the summit of Kilauea
to the south coast. These data allow us to constantly monitor the
movements of the summit and south flank regions of Kilauea and to
determine the temporal relationship between the movements. The
relevance of this study is the possible recognition of precursory
surface deformation phenomena of large earthquakes from the south
flank.
Knowing that the region is moving relatively fast (for earth surface
motion), NASA scientists use the area to test and calibrate their
technique of measuring surface deformation from space with radar
interferometry. The GPS measurements by HVO provide ground-truth to
these airborne measurements which someday may be used to routinely
monitor the surface deformation of Mauna Loa Volcano.
When you visit the lava viewing area again, you may recognize that
the steep, 2,500-foot descent down to sea level is along the fault
scarps of the Hilina fault system. The most prominent fault scarps in
the system are the Hilina, Poliokeawe, and Holei Palis.
Eruption Status
The current eruptive activity of Kilauea Volcano continues
unabated. Lava flows from the vent at the base of Pu`u `O`o through a
well-established tube system to the sea. Sporadic explosive activity
was observed at the coastal entry during the week.
One earthquake was reported felt in the past week. At 6:29 a.m. on
November 11, residents of the Volcano Golf Course subdivision were
shaken by a magnitude-3.0 temblor. The earthquake was located 3 miles
northwest of the summit of Kilauea Volcano at a depth of about 1 mile.
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