 Sign near active flows on Kilauea Volcano warning of potential hazards Photo © 2001 J.B. Paduan |
 Larger version Waikiki's landmark, Diamond Head crater, from the air Photo © 2004 J.B. Paduan |
Hazards of active volcanoes
Most of the eruptions of Hawaiian volcanoes are of the "hawaiian" style, often starting with lava fountains then becoming quietly effusive. Some flows can travel quite quickly and great distances. These eruptions pose hazards to property and unwary visitors. Occasionally, eruptions are dangerously explosive, such as Kilauea's eruptions of 1924 and 1790, which generated large volumes of ash, or the volcanism associated with the rejuvenated stage, such as created Diamond Head on Oahu. (For more on submarine explosive eruptions, see the explosive eruptions page).
Most of the earthquakes are minor, but occasionally there are large, destructive quakes, such as hit Hilo in 1973. Tsunamis from nearby as well as distant earthquakes are a serious hazard: an earthquake in Alaska in 1946 generated a tsunami that hit Hawaii some five hours later in a series of waves as high as twenty-five feet. Landslide debris found around all the islands indicates that landslides of proportions never experienced by modern Hawaiians are a grave hazard (see the landslides page).
Our research on other Hawaiian volcanic hazards
The discussions below are paraphrased from abstracts of papers published by the Submarine Volcanism group.
Earthquakes and effects on islands
HAWAII - An earthquake is a sudden movement in the Earth, occurring sufficiently quickly that the movement generates seismic waves. Basic descriptors of an earthquake are origin time, location or hypocenter, and magnitude, which are inferred by analyzing the times and amplitudes of seismic wave arrivals at recording stations equipped with seismographs. Although the vast majority of earthquakes recorded worldwide are small and are detected only by sensitive instruments that gauge the radiated seismic waves, large earthquakes can have widespread and devastating effects. Large earthquakes are also capable of triggering tsunamis when they occur at shallow depths in submarine or near-coastal regions. Earthquakes occur worldwide, but many are located on and near islands because many islands are active volcanoes or are near tectonic plate boundaries. Emergency response on islands is more difficult because of their isolation, making appropriate land use planning, adoption and enforcement of appropriate building codes, and emergency planning more critical there than elsewhere.
Reference: Okubo, P., and D.A. Clague (2009) Earthquakes, in: Encyclopedia of Islands, R.G. Gillespie and D.A. Clague (eds.), University of California Press, Berkeley, CA, pp. 240-244.
Lava emplacement on Hualalai
HAWAII - Hualalai Volcano is one of three active volcanoes on the island of Hawaii and is in its waning stage. The most recent lava flows occurred around 1800 AD and inundated coastal settlements and fishponds, and according to native accounts, King Kamehameha was called upon to stop them. A detailed field and petrologic study of these flow fields documents at least two eruptive episodes: the Hu'ehu'e flows ending in 1801 AD (visible from the Kona airport), and the Ka'upulehu flow several decades earlier. The morphology and stratigraphy of the Ka'upulehu flow indicate that it was emplaced in several days to weeks, and of the later phase of the Hu'ehu'e eruption suggest a duration of months. Based on analogies with recent eruptions at Mauna Loa and Kilauea volcanoes, the eruptions cannot have occurred at the anomalously high rate (104-105 m3/s, advancing to the coast within a few hours) as previously proposed. Studies offshore have shown that 30-50% of the erupted volume extended beyond the coastline, arguing also for a longer eruption duration.
Although neither of these flows show evidence for extraordinarily fast movement or unusual viscosities, both flows show unusual features. The abundant xenoliths (cumulates from crystallization during the tholeiitic stage of the volcano) for which the Ka'upulehu flow is famous were transported in numerous episodes of deposition and remobilization, during which they eroded the channel systems in which they traveled. Lava transport in upper and middle regions of both flow fields was through lava tubes and pahoehoe-lined channels, indicating thermally efficient transport of lava over great distances. Both flows also re-occupied older cones and lava tubes, a characteristic that may typify infrequent eruptions of older volcanic systems. Although lava flows from Hualalai Volcano do not show anomalous eruptive behavior, they pose a substantial hazard for coastal communities of Kona.
Reference: J. Kauahikaua, K.V. Cashman, D.A. Clague, D. Champion, J.T. Hagstrum (2002) Emplacement of the most recent lava flows on Hualalai Volcano, Hawaii, Bulletin of Volcanology, 64: 229-253. [Article]
Kilauea summit overflows
KILAUEA VOLCANO - The tube-fed pahoehoe lava flows covering much of the northeast flank of Kilauea Volcano are named the 'Aila'au flows. Their eruption age, based on radiocarbon dates, is approximately AD 1445. The flows have distinctive paleomagnetic directions with steep inclinations (40-50°) and easterly declinations (0-10°E). The lava was transported ~40 km from the vent to the coast in long, large-diameter tubes; the longest tube (Kazumura Cave) reaches from near the summit to within several kilometers of the coast near Kaloli Point. The estimated volume of the 'Aila'au flow field is 5.2+0.8 km3, and the eruption that formed it probably lasted for 50 years.
Summit overflows from Kilauea may have been nearly continuous between ~AD 1290 and 1470, during which time a series of shields formed at and around the summit. The 'Aila'au shield was either the youngest or next to youngest in this series of shields. The older flows range from 2750 to <18,000 years in age. The region was inundated by flows only three times in the past 5000 years. The intervals between eruptions average ~1600 years. Lava flows from most of the summit eruptions also reached the coast, but none appears as extensive as the 'Aila'au flow field. The chemistry of the melts during these summit overflows is remarkably similar, averaging ~6.3 wt% MgO near the coast and 6.8 wt% near the summit. The present-day caldera probably formed more recently than the eruption of the 'Aila'au flows. The earliest explosive eruptions that formed the Keanakako'i Ash, which is stratigraphically above the 'Aila'au flows, cannot be older than about AD 1470.
Reference: D.A.Clague, J.T. Hagstrum, D.E. Champion, and M.H. Beeson (1999) Kilauea summit overflows: their ages and distribution in the Puna District, Hawaii, Bulletin of Volcanology, 61: 363-381. [Article]
Clastic deposits in Hilo drill core
HILO - Volcaniclastic units cored at depths of about 87, 164, 178, 226, and 246 meters below sea level and carbonate units located between depths of 27 and 53 meters below sea level in the Hilo drill core were found to be deposited at or near sea level. Four of these unites are hydroclastic deposits, formed when subaerially erupted Mauna Loa lava flows entered the ocean and fragmented to produce quenched, glassy fragments during hydrovolcanic explosions. Ash units 24 and 26, at 178 meters depth, accumulated at sea level in a freshwater bog. They contain pyroxenes crystallized from tholeiitic magma that we infer erupted explosively at the summit of Kilauea volcano. Two carbon-rich layers from these ashes have a weighted average radiocarbon age of 38.6 + 0.9 thousand years; the ashes probably correlate with the oldest and thickest part of the Pahala ash. Ash unit 44, at the transition from Mauna Kea to Mauna Loa lava flows, was probably nearly 3.2 meters thick and is inferred to be equivalent to the lower thick part of the composite Homelani ash mapped in Hilo and on the flanks of Mauna Kea. The age of this part of the Homelani ash is between 128 + 33 and 200 + 10 thousand years; it may have erupted subglacially during the Pohakuloa glacial maximum on Mauna Kea. Beach sand units 1 and 22 were derived from nearby Mauna Loa and Mauna Kea lava flows. The middle of beach sand unit 38 was derived mainly from lava erupted near the distal end of the subaerial east rift zone of Kilauea volcano; these sands were transported about 33 km northwest to Hilo Bay by prevailing longshore currents.
Combined age, depth, and sea level markers in the core allow us to determine that lava flow recurrence intervals averaged one flow every 4000 years during the past 86 thousand years and one flow every 16,000 years between 86 and 200 thousand years at the drill site and that major explosive eruptions that deposit thick ash in Hilo have occurred only twice in the last 400,000 years. These recurrence intervals support the moderate lava flow hazard zonation (zone 3) for coastal Hilo previously determined from surficial mapping.
Reference: M.H. Beeson, D.A. Clague, and J.P. Lockwood (1996) Origin and depositional environment of clastic deposits in the Hilo drill hole, Hawaii, Journal of Geophysical Research, 101(B5): 11617-11629. [Article]
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