Tsunami, Earthquakes, Hurricanes, Volcanic Eruptions and other Natural and Man-Made Hazards and Disasters - by Dr. George Pararas Carayannis

Tsunami, Earthquakes, Hurricanes, Volcanic Eruptions and other Natural and Man-Made Hazards and Disasters

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INSTABILITY OF KILAUEA VOLCANO'S SOUTHERN FLANK - EVALUATION OF MASS EDIFICE FAILURES, FLANK COLLAPSES AND POTENTIAL TSUNAMI GENERATION

George Pararas-Carayannis

Copyright © 2005. All Rights Reserved

Introduction

Throughout Kilauea volcano's geologic history there have been numerous mass edifice failures, collapses and subsidence along its southern flank - some associated with earthquakes and local destructive tsunamis such as those of 2 April 1868 and 29 November 1975.

There is geologic evidence of a zone of weakness along the volcano's southern flank. Paralleling the Puna rift zone is an extensive system of coastal faults (palis), which appear to be gravitational features associated with ongoing subsidence caused by both seismic and aseismic events - the latter also documented by recent GPS satellite measurements. There is also evidence of other parallel submarine volcanic rift zones formed in an evolutionary sequence. The following report evaluates:


a) The instability of Kilauea' southern flank;
b) On going subsidence and kinematic processes;
c) Crustal displacements associated with flank failures of the southern flank
d) Expected future failures and frequency of recurrence
e) Tsunami generation mechanisms of oceanic shield stratovolcanoes in general;
f) Tsunami generation efficiency of volcanic flank failures; in particular: and,
g) Tsunami generation from Kilauea's past and future flank failures.

The Instability of Kilauea's Southern Flank

Marine geophysical data, including SEA BEAM bathymetry, HAWAII MR1 sidescan, and seismic reflection profiles, indicate that the southern slope of the Island of Hawaii comprises of the three active hot spot volcanoes, which are Mauna Loa, Kilauea and the submarine volcano Loihi. This is the locus of the Hawaiian hot spot (Smith et al, 1999).

Review of the coastal geology along Kilauea's southern flank, indicates a complex pattern of kinematic processes and of resulting geomorphological features.

A number of large coastal fault scarps (palis), some as high as 500 meters, parallel the Puna rift zone and are the tops of an extensive fault zone along which substantial movement has occurred in the past. Large fault blocks are tilted back, by as much as 8 degrees towards the rift zone, indicating a pattern of gradual subsidence. This continuous subsidence has created the feature known as the Hilina Fault System.

Hawaii's southern slope showing coastal faults parallel to the east rift zone of the Kilauea volcano, and the Hilina Slump along which slope failures have been occurring (Modified after Morgan et al. 2001).

The Hilina Slump and the Papa`u Seamount - The Hilina Slump and the Papa`u Seamount are the offshore continuation of the mobile Kilauea volcano's south flank that has resulted from extensive subsidence and slope failure along a deeper detachment surface. (Morgan et al 2001).

High-resolution side scan surveys of Kilauea's southern slope (Clague et al 1998; Dartnell and Gardner 1999) show a number of cuspate normal faults near the head of the Slump, as well as grabens and horsts in the offshore region. These are indicative of past successive, crustal movements - some associated with major earthquakes.

Presently, the sub-aerial portion of the Slump creeps seaward at a rate of approximately 10 cm/year. It is presumed that the underwater portion is also moving at the same rate.

Also, review of the submarine geology of the Island of Hawaii shows evidence of debris avalanches on the ocean floor along the southwestern flank of the Mauna Loa and the southern flank of Kilauea. The debris avalanches are indicative of large prehistoric slides (Moore et al. 1989, 1994; Lipman, 1995; Moore and Chadwick, 1995; Clague et al., 1998; Dartnell and Gardner, 1999).

Crustal Displacements Associated with Flank Failures of Kilauea's Southern Flank

Crustal movements associated with flank failures of Kilauea volcano's southern flank appear to involve uplift, subsidence and slope failure along the Hilina Slump. The most recent and extensively studied event was the flank failure associated with the Kalapana tsunamigenic earthquake of 29 November 1975.

The Flank Failure of 29 November 1975 - The 1975 flank failure uplifted the sea floor offshore as the onshore section of the volcano down-dropped and moved outward. Post-earthquake surveys showed that a large crustal block slid horizontally towards the ocean but that there was a great deal of variation in the degree of crustal displacements (Pararas-Carayannis 1975). The maximum horizontal displacement, near Keauhou Landing several kilometers east of Halape, was about 26 feet. The displacements decreased to the east and west from this area. The dimensions of the sea floor affected by the crustal movements of the 29 November 1975 flank failure were approximately 70 km long, and 30 km wide with the long axis of the displaced block being parallel to the coast. This entire offshore region rose approximately 1.2 meters (3.9 feet). The total volume of displaced material was roughly estimated to be only 2.52 cubic km (Pararas-Carayannis 1976a,b). These appear to be typical displacements associated with flank failures of Kilauea's southern flank.

Oblique sidescan view of the Papa`u Seamount (Modified after Smith et al, 1999)

Inspection of tide gauge records of the tsunami on the Island of Hawaii and the other islands indicated that the initial tsunami wave motion from this flank failure was upwards at all stations. This confirmed also that the initial offshore crustal displacement for this volcanic flank failure was a uplift, as the onshore section subsided and moved outward. This also supported the conclusion that the resulting slope failure and earthquake were not entirely due to gravitational effects of instability, but may have been partially caused by compressional lateral magma migration from shallow magmatic chambers of Kilauea, or by lateral magmastatic forces along an arcuate failure surface,or along a secondary zone of crustal weakness on the upper slope of the Hilina Slump. In fact, recent paleomagnetic studies show that differential rates of movement and rotation occur between sections of the Hilina Slump (Riley et al., 1999). Also, this had become evident during the survey of crustal displacements associated with the 29 November 1975 event (Pararas-Carayannis 1975).

Kinematic Movements Associated With Kilauea's Flank Failures

Seismic studies indicate that Kilauea is sliding along the seafloor or along parallel zones of weakness within the southern rift zone, thus creating the Hilina Slump. Because of such movement cuspate normal faults have been formed near the head of the Slump. Also, the paleomagnetic studies of changes in lava flow directions on the Hilina Fault scarps have helped determine the pattern and speed of subsidence and kinematic movement along the southern flank of the volcano. In addition to subsidence, these studies have determined a pattern of counterclockwise rotation, indicating slippage between blocks, occurring along listric normal faults (Riley et al., 1999).

Submarine Topography of the Loihi Volcano (Alexander Malahoff graphic)

As previously stated, during the 1990's Kilauea appeared to be sliding easily along its base in a seaward direction at an average speed of about 10 cm a year. When this movement is blocked large earthquakes occur. The growth of the submarine volcano Loihi has formed a boundary to the southwest, which appears to limit Hilina's failure and movement in that direction.

 

The Aseismic Slip of November 2000 ­ Aseismic kinematic movements and slippage of the Hilina block were measured by satellites of the Global Positioning System (GPS) in November 2000. The measurements documented that a 12- by 6-mile area (amounting to about 72-square-miles) of the south slope of Hawaii's Kilauea Volcano moved 3.5 inches toward the sea, over a 36-hour period.

Although indicative of instability, the motions were imperceptible and occurred along the upper slope of Kilauea's southern flank (Cervelli et al, 2000). Such slow aseismic movements have probably occurred over thousands of years. These imperceptible kinematic changes are now being detected and measured on a regular basis only because the new satellite technology and instrumentation have made it possible.

Triggering Mechanisms of Kilauea Volcano's Flank Failures

Volcanic flank failures can be triggered by isostatic load adjustments, extensive erosion, gaseous pressures, violent phreatomagmatic eruptions, magmastatic pressures, gravitational collapse of magmatic chambers, dike and cryptodome intrusions as well as buildup of hydrothermal and supra hydrostatic pore fluid pressures. For a more complete discussion of triggering mechanisms of volcanic flank failures and gravitational flank collapses of island stratovolcanoes go to http://drgeorgepc.com/ TsunamiMegaEvaluation.

For this report it will suffice to discuss only the most common triggering mechanisms of major flank failure for shield volcanoes such as Kilauea. The primary triggering mechanisms of Kilauea's flank failure appear to be mechanical magma intrusion, magmastatic pressures and lava dike intrusions. Isostacy may also play a significant role but there is no sufficient data to determine its influence.

The south flank of the Kilauea volcano is characterized by frequent, low-intensity seismicity. Most of the sudden crustal movements which have generated occasional strong shallow earthquakes in the past appear to be triggered by sudden flank failures caused by magmatic intrusions and lava movements.

Essentially, the movement of magma in the volcanic chambers acts as a piston in creating hydraulic pressure - mainly upwards but also laterally. Such pressure spreads the volcano's base. Lava moving higher in the volcanic dikes along a rift zone exerts lateral as well as vertical pressures. Compression by such magma and lava movements can push large crustal blocks outward and trigger substantial coastal crustal displacements and shallow-focus tsunamigenic earthquakes. The many grabens and horsts on the southern offshore flank of Kilauea are indicative of such gradual failure events. These submarine geomorphological features parallel the Kau rift zone and are as indicative of compression activity.

Also, similar lava movements or gravitational settling, by activity termed as "silent earthquakes" may induce gradual coastal subsidence. As reported above, the November 2000 aseismic slippage detected by the satellites of the Global Positioning System is indicative of such gradual movement and settling along the south slope of Hawaii's Kilauea Volcano.

Either process is capable of triggering larger underwater slumps or landslides. The Hilina slump on the southern slope of Kilauea and the Koolau slumps off the Island of Oahu are some of the larger scale features of underwater slope failures that appear to have been triggered by such mechanisms. Whether these are singular, sudden events, or composite events that have occurred over a period of time, will be analyzed and discussed in detail in another report.

Future Failures of Kilauea Volcano's Southern Flank

Kilauea is being actively monitored by satellite instrumentation which permits accurate geodetic measurements and of rates of movement along its south flank. These measurements indicate that stresses are building up at the present time. Once a threshold limit is exceeded; there will be another release of accumulated energy along the volcano's southern flank. Magmatic pressures from within Kilauea's own chambers or lava dike intrusion will probably trigger such failures. Pressures from within Mauna Loa's magmatic chambers may also contribute to instability and future failure of Kilauea's southern flank.

In spite of such apparent instability, a massive flank failure of Kilauea along a detachment fault zone - as postulated (Ward 2001) - is very unlikely to occur. Neither the 1868 nor the 1975 earthquakes were associated with massive flank failures of Mauna Loa or Kilauea or generated an ocean-wide mega tsunami (Pararas-Carayannis 1976a, 1976b, 2002; Pararas-Carayannis and Calebaugh, 1977).

Future mass edifice failure events and major flank collapses of Kilauea's south flank can be expected to result in large, shallow focus earthquakes on a nearly flat-lying fault plane. A repeat of the 1975 flank failure and associated large earthquake, can be expected on the south flank of Kilauea every 200 years or even more frequently (Pararas-Carayannis,1976a,b). Smaller events can be expected to occur every 100 years more or less - depending on volcanic activity and internal pressure build up. Most failures will occur as discreet events ­ perhaps over a period of time.

Tsunami Generation Mechanisms of Oceanic Shield Volcanoes

Since shield volcanoes are normally characterized by sporadic and weak explosive activity, tsunamis cannot be effectively generated by their eruptions. However, near the coast, secondary eruptions associated with explosive phreatomagmatic activity known as Surtseyan, can generate small local tsunamis. For example, the small cones of Diamond Head, Coco Head and Punchbowl are examples of secondary activity of the Koolau volcano on the island of Oahu.

These violent Surtseyan eruptions occurred in the last 10,000-40,000 years. The small fragments of coral, which can still be seen embedded within the consolidated, volcanic ash, indicate the strength of their explosive activity. Each of these violent phreatomagmatic eruptions lasted only a few hours, with some extreme episodes, which, undoubtedly, generated local tsunamis.

Larger and more destructive local tsunamis may be also generated by the mass edifice failure and collapses of the flanks of active oceanic shield volcanoes such as Kilauea. As previously discussed, the evolutionary development of such volcanoes generates lateral forces at right angles to the major rift zones, forcing volcanic mass outward and thus triggering faulting subsidence and flank collapses.

Though most of the collapse processes of shield volcanoes are closely associated with regional volcanic activity, slow aseismic tectonic subsidence and gravitational isostatic settling can occur also along fractures controlled by regional fault patterns as described previously. The fault patterns may be localized along ring fractures and may indeed form circular caldera-like depressions which may continue underwater - as at the Piton De La Fournaise volcano on Reunion Island in the Indian Ocean, or as extensive flank rifts as along the southern part of the volcanoes of Santorin or Kilauea.

An arcuate coastline on a volcanic island may be indicative of such failure along a ring dike, or along a rift zone. Such coastal slope failures may be triggered concurrently or subsequently to an eruption. Interstitial ground water saturation, gravitational settling, or tectonic earthquakes along major fracture zones, can also trigger sizeable flank failures and thus generate tsunamis - often independently of eruptive processes. Earth tides and oceanic tidal loading may also play a role in triggering volcanic flank failures.

Such flank failures may be massive and be associated with major earthquakes and large local tsunamis. However, the focal depths of such earthquakes are normally fairly shallow and most of the destruction is caused by the tsunami. The extent of the crustal displacements associated with these failures may range from moderate to large and may occur in phases over a period of time, rather than as single discreet events. Thus, one or more tsunamis may be generated. Other factors may limit the extent of flank failures.

For example, oceanic shield stratovolcanoes - such as Kilauea - have underwater slopes composed primarily of fairly stable pillow lavas with a smaller percentage of unstable pyroclastics. As already described, collapses and flank failures can be expected to occur periodically. However, most of these failures may be distinct, rather than massive events. They may result from step faulting such as that along the Hilina slide on the southern underwater slope of Kilauea. The following is an evaluation of flank failures of shield stratovolcanoes such as Kilauea, and of the mechanisms of tsunami generation of such processes.

Tsunami Generation Efficiency of Volcanic Flank Failures

The efficiency of tsunami generation depends on the volume of crustal material involved in the slope failure and on its time history, speed and efficiency of coupling with water displacement. Although such slope failures can be expected to generate destructive local tsunamis, the source dimensions would result in waves of relatively short wavelength and period. The energy and height of tsunami waves would attenuate rapidly away from the source.

Finally, earthquakes induced by movement of lava in the magmatic chambers of a volcano may result in compressional effects and cause both coastal subsidence and offshore uplift - with the formation of underwater grabens and horsts along the southern slope of Kilauea. However, because of the relatively shallow depth of such earthquakes, small area extent, and the relatively small volume of crustal displacements, the resulting tsunamis have relatively short periods. Their destructiveness is usually confined in the immediate area of generation.

Tsunami Generation from Flank Failures of the Kilauea Volcano

Slope failures and subsidence along Kilauea southern flank have occurred with frequency in the past. The failures appear to occur in phases over a period of time, rather than as single, large-scale events involving great volumes of crustal material. Other, large scale hydromagmatic explosions, like those of Krakatoa, Santorin or Tambora, also occur in stages but are usually associated with different mechanisms which are presented elsewhere at this website. Also to be discussed separately and evaluated in the future, will be the postulated massive Koolau slide off the eastern coast of the island of Oahu.

The rarer and more massive volcanic flank failures can be expected to result in voluminous crustal displacements and debris avalanches which may extend to the ocean floor and form large debris toes. There is evidence of such a toe and debris along the southeastern end of the Hilina Slide. Although an isopach has not been constructed, the volume and dimensions of this prehistoric slide do not appear to be as great, as that of 1868 along the flank of the Mauna Loa volcano.

As indicated previously, inspection of the offshore bathymetry of the southern coastal region of the island of Hawaii reveals a pattern of "horsts" and 'grabens" - topographical features suggestive of a long history of large crustal block movements, subsidence and flank failures. These features parallel the displacements on land (the palis).

Thus, mass edifice failures appear to have occurred with regularity along Kilauea's southern flank. Magmatic movements near the magmatic chambers of Kilauea's Puna Volcanic rift zone induce most failures and associated earthquakes. Such failures must have generated destructive tsunamis in prehistoric times, and as recently as 1868 and 1975. Even smaller failures occurred as recently as 1989. These resulted in smaller but still damaging earthquakes but did not generate tsunamis. There was no apparent evidence of slope instability and failure. The ocean slope of the island consists primarily of pillow lavas - not particularly susceptible to large-scale slope failures. Slope failures can occur but not necessarily as single, large scale events. The geomorphology of the Hilina slump indicates slope failures, which occurred as a series of discrete events over a period of time.

The movement of lava in the magmatic chambers below a shield volcano, by acting as a piston, has the potential of inducing shallow focus earthquakes with substantial coastal crustal displacement. For example, offshore submarine geomorphological features, such as the grabens and horsts observed south of the volcano of Kilauea and paralleling the Kay rift zone, are indicative of such activity. Such volcanic earthquakes near the coast have the potential of generating very destructive local tsunamis. However, because of the relatively shallow depth of the earthquake and the relatively small volume of crustal displacements, tsunamis destructiveness is usually confined in the immediate area of generation.

The destructive local tsunamis of August 29, 1975 on the southern coast of the island of Hawaii is an example of such activity. There was no tsunami of significance outside the source region. Although there was extensive coastal subsidence along the southern coast, the first wave motions of the tsunami were up, indicating offshore uplift.

In contrast, the first water motions of the destructive, local April 2,1868 tsunami were down, indicating tsunami generation entirely by subsidence, or slope failure, along the underwater slope of Mauna Loa rather than Kilauea. Maximum coastal subsidence occurred somewhat westward of the 1975 event. The main event was preceded by a series of small earthquakes caused by significant magmatic movements. Also, there was a flank eruption of Mauna Loa.

Conclusions

In summary, there is no indication that Kilauea's southern flank is unusually unstable at this time or that a catastrophic massive failure will occur soon. The subsidence process on the Hilina Slump appears to be continuous and gradual. The 1975 flank failure and major earthquake generated only a local destructive tsunami along the southern coast. with limited far field effects elsewhere in the Hawaiian Islands and the Pacific.

However, a major crustal adjustment can be expected to occur again on Kilauea's southern flank in the future. Such an event could occur in the mid-21st Century or even sooner - unless the stresses that are building up presently are relieved by aseismic slippage. When a flank failure occurs again a major earthquake with an upper magnitude limit of about 7.4 can be expected. As with the 1868 and the 1975 events a very destructive local tsunami will be generated.

REFERENCES

Cervelli, et al., 2000. Sudden aseismic fault slip on the South Flank of Kilauea volcano. (at web site *).

Clague, D. A., Reynolds, J. R., Maher, N., Hatcher, G., Danforth, W., and Gardner, J. V., 1998. High-Resolution Simrad EM300 Multibeam Surveys Near the Hawaiian Islands: Canyons, Reefs, and Landslides. EOS, Transactions American Geophysical Union, 79, F826.

Dartnell, P. and J.V. Gardner (1999). Sea-Floor Images and Data from Multibeam Surveys in San Francisco Bay, Southern California, Hawaii, the Gulf of Mexico, and Lake Tahoe, California-Nevada, [CD-ROM]. Washington, D.C.: U.S. Geological Survey (Digital Data Series, DDS-55.Version 1.0).

Morgan, J.K., Moore, G.F., and Clague, D.A., 2001, Papa`u Seamount: the submarine expression of the active Hilina Slump, south flank of Kilauea Volcano, Hawaii. Journal of Geophysical Research, submitted.

Pararas-Carayannis, George. Catalog of Tsunamis in the Hawaiian Islands. Data Report Hawaii Inst.Geophys. Jan. 1968

Pararas-Carayannis, George. Catalog of Tsunami in the Hawaiian Islands. World Data Center A- Tsunami U.S. Dept. of Commerce Environmental Science Service Administration Coast and Geodetic Survey, May 1969.

Pararas-Carayannis, G. , 1976a. The Earthquake and Tsunami of 29 November 1975 in the Hawaiian Islands. ITIC Report, 1976.

Pararas-Carayannis, G., 1976b. In International Tsunami Information Center - A Progress Report For 1974-1976. Fifth Session of the International Coordination Group for the Tsunami Warning System in the Pacific, Lima, Peru, 23-27 Feb. 1976

Pararas-Carayannis, G and Calebaugh P.J., 1977. Catalog of Tsunamis in Hawaii, Revised and Updated, World Data Center A for Solid Earth Geophysics, NOAA, 78 p., March 1977.

Pararas-Carayannis, G, 1988. Risk Assessment of the Tsunami Hazard. In Natural and Man-Made Hazards, 1988, D. Reidal, Netherlands, pp.171-181.

Pararas-Carayannis, George, Evaluation of the Threat of Mega Tsunami Generation from Postulated Massive Slope Failures of Island Stratovolcanoes on La Palma, Canary Islands, and on the Island of Hawaii, Science of Tsunami Hazards. Vol 20 (5). pages 251-277, 2002

Riley C. M. , Diehla, J. F. Kirschvink J. L. andRipperdanc, R. L. 1999. Paleomagnetic constraints on fault motion in the Hilina Fault System, south flank of Kilauea Volcano, Hawaii. Journal of Volcanology and Geothermal Research, Vol. 94 (1-4) (1999) pp. 233-249

Smith, J. R. Malahoff A., and Shor A. N., 1999. Submarine geology of the Hilina slump and morpho-structural evolution of Kilauea volcano, Hawaii. Journal of Volcanology and Geothermal Research, V. 94, No 1-4, 1, pp. 59-88 December

Ward, S. N., 2001. Landslide Tsunami. J. Geophys. Res., Accepted and In Press.

Moore, J.G., Clague, D.A., Holcomb, R.T., Lipman, P.W., Normark, W.R., and Torresan, M.E., 1989., Prodigious submarine landslides on the Hawaiian Ridge. Journal of Geophysical Research, Series B 12, Volume 94, p. 17,465-17,484. 94, 17,465-17, 484.

Moore, J.G., and Chadwick, W.W. Jr., 1995, Offshore geology of Mauna Loa and adjacent areas, Hawaii. In Geophysical Monograph 92, Mauna Loa Revealed: structure, composition, history, and hazards, ed. by J.M. Rhodes and J.P. Lockwood, American Geophysical Union, Washington, D.C., p. 21-44.

Moore, J.G., and Clague, D.A., 1992. Volcano growth and evolution of the island of Hawaii. Geologic Society of America Bulletin, 104, 1471-1484.

Moore, J.G., Normark, W.R. & Holcomb, R.T., 1994. Giant Hawaiian Landslides. Annual Reviews of Earth and Planetary Science, 22, 119-144.

Reynolds, J. R., Clague, D.A., Hatcher, G. and Maher, N., 1998. Evolutionary Sequence of Submarine Volcanic Rift zones in Hawaii. EOS, Transactions American Geophysical Union, 79, F825.

U.S. Geological Survey, Hawaii Volcano Observatory, Survey of the 29 November 1975 Earthquake

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