Jim Kauahikaua

Emplacement and inflation of pahoehoe sheet flows: Observations and measurements of active lava flows on Kilauea Volcano, Hawaii

Inflated pahoehoe sheet flows have a distinctive horizontal upper surface, which can be several hundred meters across, and are bounded by steep monoclinal uplifts. The inflated sheet flows we studied ranged from 1 to 5 m in thickness, but initially propagated as thin sheets of fluid pahoehoe lava, generally 20-30 cm thick. Individual lobes originated at outbreaks from the inflated front of a prior sheet-flow lobe and initially moved rapidly away from their source. Velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow. As the outward flow velocity decreases, cooling promotes rapid crustal growth. At first, the crust behaves plastically as pahoehoe toes form. After the crust attains a thickness of 2-5 cm, it behaves more rigidly and develops enough strength to retain incoming lava, thus increasing the hydrostatic head at the flow front. The increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow, resulting in uniform uplift of the entire sheet-flow lobe. Initial uplift rates are rapid (flows thicken to 1 m in 1-2 hours), but rates decline sharply as crustal thickness increases, and as outbreaks occur from the margins of the inflating lobe. One flow reached a final thickness of nearly 4 m after 350 hr. Inflation data define power-law curves, whereas crustal cooling follows square root of time relationships; the combination of data can be used to construct simple models of inflated sheet flows. As the flow advances, preferred pathways develop in the older portions of the liquid-cored flow; these pathways can evolve into lavatube systems within a few weeks. Formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1-2 orders of magnitude slower. If advance of the sheet flow is terminated, the tube remains filled with lava that crystallizes in situ rather than draining to form the cave-like lava tubes commonly associated with pahoehoe flows. Inflated sheet flows from Kilauea and Mauna Loa are morphologically similar to some thick Icelandic and submarine sheet flows, suggesting a similar mechanism of emplacement. The planar, sheet-like geometry of flood-basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava.

Development of the 1990 Kalapana Flow Field, Kilauea Volcano, Hawaii

The 1990 Kalapana flow field is a complex patchwork of tube-fed pahoehoe flows erupted from the Kupaianaha vent at a low effusion rate (approximately 3.5 m3/s). These flows accumulated over an 11-month period on the coastal plain of Kilauea Volcano, where the pre-eruption slope angle was less than 2°. the composite field thickened by the addition of new flows to its surface, as well as by inflation of these flows and flows emplaced earlier. Two major flow types were identified during the development of the flow field: large primary flows and smaller breakouts that extruded from inflated primary flows. Primary flows advanced more quickly and covered new land at a much higher rate than breakouts. The cumulative area covered by breakouts exceeded that of primary flows, although breakouts frequently covered areas already buried by recent flows. Lava tubes established within primary flows were longer-lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply; tubes within breakouts were never reoccupied once the supply was interrupted. During intervals of steady supply from the vent, the daily areal coverage by lava in Kalapana was constant, whereas the forward advance of the flows was sporadic. This implies that planimetric area, rather than flow length, provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes.

Deep magmatic structures of Hawaiian volcanoes, imaged by three-dimensional gravity models

A simplified three-dimensional model for the island of Hawai9i, based on 3300 gravity measurements, provides new insights on magma pathways within the basaltic volcanoes. Gravity anomalies define dense cumulates and intrusions beneath the summits and known rift zones of every volcano. Linear gravity anomalies project southeast from Kohala and Mauna Kea summits and south from Hualālai and Mauna Loa; these presumably express dense cores of previously unrecognized rift zones lacking surface expression. The gravity-modeled dense cores probably define tholeiitic shield–stage structures of the older volcanoes that are now veneered by late alkalic lavas. The three-dimensional gravity method is valuable for characterizing the magmatic systems of basaltic oceanic volcanoes and for defining structures related to landslide and seismic hazards.

One hundred years of volcano monitoring in Hawaii

In 2012 the Hawaiian Volcano Observatory (HVO), the oldest of five volcano observatories in the United States, is commemorating the 100th anniversary of its founding. HVOs location, on the rim of Kīlauea volcano (Figure 1)—one of the most active volcanoes on Earth—has provided an unprecedented opportunity over the past century to study processes associated with active volcanism and develop methods for hazards assessment and mitigation. The scientifically and societally important results that have come from 100 years of HVOs existence are the realization of one mans vision of the best way to protect humanity from natural disasters. That vision was a response to an unusually destructive decade that began the twentieth century, a decade that saw almost 200,000 people killed by the effects of earthquakes and volcanic eruptions.

GIS-Aided Volcanic Activity Hazard Analysis for the Hawaii Geothermal Project Environmental Impact Statement

Vector-based GIS computer systems are used with digital geologic maps of the active volcanoes of Kilauea and Mauna Loa, Hawai‵i to assess the probability that activity from those volcanoes might adversely affect the wells, power plants, and transmission lines of the Hawaii Geothermal Project. For each of the geothermal subzones, the probability of inundation by lava flows is 64–65%. For the three possible transmission line routes, the proposed has an 86% probability, the first alternate has a 63% probability, and the second alternate has a 28% probability of lava flow inundation. On the basis of this analysis, the second alternate transmission line route is the least likely to be damaged by a lava flow.