USGS Science⌕ Search

Geology topics

R. Y. Koyanagi

Publications and source records attributed to R. Y. Koyanagi.

13 recordsLinked to original sources
USGS1991

Volcanologic investigations in the Commonwealth of the Northern Mariana Islands, September-October 1990

U.S. Geological Survey volcanologists examined the ten volcanoes in the active Mariana Arc north of Saipan in May 1992, at the request of the Governor and the Disaster Control Office of the Commonwealth of the Northern Mariana Islands (CNMI). A shallow earthquake swarm on Anatahan in March-April 1990 and reports of possible new fuming on Agrigan in August 1990 had prompted the evacuation of all CNMI islands north of Saipan. None of the volcanoes in the chain erupted during our visit. Five uninhabited islands (Farallon de Pajaros, Maug, Asuncion, Guguan, and Sarigan) were inspected only from the air, while the other four were studied in more detail. The previously installed seismic stations on Anatahan, Alamagan, and South Pagan were upgraded. A new station was established at the southwestern base of the intermittently active Mount Pagan, on the northern end of Pagan Island. Portable seismometers were operated on Anatahan, Alamagan, Pagan, and Agrigan. The seismometers on Anatahan, Alamagan, and Agrigan recorded no local shallow earthquake swarms nor volcanic tremor indicative of shallow magmatic movement. On Mount Pagan, intermittent low-amplitude tremor indicated the continuing possibility of occasional small ash eruptions, which prior to our visit had been witnessed in April 1992. Ash eruptions resumed in February 1993. Electronic distance measurement (EDM) lines were remeasured on Agrigan, Mount Pagan, and Anatahan. Line length changes were generally insignificant, in accord with the absence of significant shallow seismicity. Hot spring waters were collected on Agrigan, Pagan, and Anatahan, and fumarole temperatures were measured on Agrigan, Pagan, Alamagan, and Anatahan. The temperature data showed no indication of an impending significant change in the state of these volcanoes. We mapped the geology of Alamagan, collected charcoal to date eruptions of Alamagan and Mount Pagan, and collected rocks on Agrigan, Pagan, Alamagan, and Anatahan for petrographic and chemical studies. We conclude that the low shallow seismicity, lack of significant deformation, and low fumarole temperatures suggest that no eruption is likely soon on Agrigan, Alamagan, or Anatahan. The persistent low-level volcanic tremor on Mount Pagan suggests that intermittent small explosive eruptions may continue to occur.

Open-File Report↗
USGS1986

Mechanical response of the south flank of Kilauea volcano, Hawaii, to intrusive events along the rift systems

Increased earthquake activity and compression of the south flank of Kilauea volcano, Hawaii, have been recognized by previous investigators to accompany rift intrusions. We further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major rift intrusions which occurred between December 1971 and January 1981. The seismic response of the south flank to individual rift intrusions is immediate; the increased rate of earthquake activity lasts from 1 to 4 weeks. Horizontal strain measurements indicate that compression of the south flank usually accompanies rift intrusions and eruptions. Emplacement of an intrusion at a depth greater than about 4 km, such as the June 1982 southwest rift intrusion, however, results in a slight extension of the subaerial portion of the south flank. Horizontal strain measurements along the south flank are used to locate the January 1983 east-rift intrusion, which resulted in eruptive activity. The intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet. This model suggests that the intrusive body that compressed the south flank in January 1983 extended from the surface to about 2.4 km depth, and was aligned along a strike of N66°E. The intrusion is approximately 11 km in length, extended beyond the January 1983 eruptive fissures, which are 8 km in length and is contained within the 14-km-long region of shallow rift earthquakes.

Hawaii↗
USGS1984

The eruption of Mount Pagan volcano, Mariana Islands, 15 May 1981

A major explosive eruption occurred 15 May 1981 at Mount Pagan Volcano, the larger of two historic eruptive centers on Pagan Island, Mariana Islands. The eruption was preceded by increased numbers of locally felt earthquakes beginning in late March or early April and by new ground cracks, new sublimates, and increased gas emissions. A swarm of felt earthquakes began at 0745h (local time = UCT+10 hours) 15 May, and at 0915 h, closely following a loud sonic boom, a strong plinian column issued from the volcano. The high-altitude ash cloud (at least 13.5 km) travelled south-southeast, but ash and scoria deposits were thickest (> 2 m) in the NW sector of the island because of the prevailing low-altitude southeasterly winds. The early activity of 15 May probably involved magmatic eruption along a fissure system oriented about N10??E. However, the eruption became hydromagmatic, possibly within minutes, and was largely restricted to three long-lived vents. The northernmost of these built a substantial new scoria-ash cinder cone. Flows and air-fall deposits, consisting almost entirely of juvenile material, exceeded 105 ?? 106 m3 in volume (75 ?? 106 m3 of magma) on land and at least 70-100 ?? 606 m3 at sea. An unknown volume was carried away by stratospheric winds. Lithic blocks and juvenile bombs as large as 1 m in diameter were thrown more than 2 km from the summit, and evidence for base-surge was observed in restricted corridors as low as 200 m elevation on the north and south slopes of the volcano. Neither of these events resulted in serious injuries to the 54 residents of the island, nor did the eruption produce serious chemical hazards in their water supply. Weak eruptions occurred during the ensuing month, and some of these were monitored by ground observations, seismic monitoring, and deformation studies. Precursory seismicity and possibly deformation occurred with some of the observed eruptions. More vigorous eruptions were reported by visiting residents in late 1981 and early 1982, but these were of lesser magnitude than the 15 May 1981 event. The 15 May lava is predominantly aa and ranges from 3 to > 30 m in thickness. In composition, it is a high-alumina basalt with small (< 1 mm long) phenocrysts of plagioclase and clinopyroxene (7%) that is more or less typical of basalt of the northern Marianas volcanoes. It contains slightly more SiO2 (52%), K2O, TiO2, and less Al2O3 and CaO than does the basalt of the last eruptive event of Mount Pagan Volcano in 1925. Gas analyses indicate that a large portion of air was introduced into the vent system through the porous volcanic edifice and that the carbon gases were not in equilibrium with the magma or each other. ?? 1984.

Journal of Volcanology and Geothermal Research↗
USGS1980

The 1977 eruption of Kilauea volcano, Hawaii

Kilauea volcano began to erupt on September 13, 1977, after a 21.5-month period of quiescence. Harmonic tremor in the upper and central east rift zone and rapid deflation of the summit area occurred for 22 hours before the outbreak of surface activity. On the first night, spatter ramparts formed along a discontinuous, en-echelon, 5.5-km-long fissure system that trends N70??E between two prehistoric cones, Kalalua and Puu Kauka. Activity soon became concentrated at a central vent that erupted sporadically until September 23 and extruded flows that moved a maximum distance of 2.5 km to the east. On September 18, new spatter ramparts began forming west of Kalalua, extending to 7 km the length of the new vent system. A vent near the center of this latest fissure became the locus of sustained fountaining and continued to extrude spatter and short flows intermittently until September 20. The most voluminous phase of the eruption began late on September 25. A discontinuous spatter rampart formed along a 700-m segment near the center of the new, 7-km-long fissure system; within 24 hours activity became concentrated at the east end of this segment. One flow from the 35-m-high cone that formed at this site moved rapidly southeast and eventually reached an area 10 km from the vent and 700 m from the nearest house in the evacuated village of Kalapana. We estimate the total volume of material produced during this 18-day eruption to be 35 ?? 106 m3. Samples from active vents and flows are differentiated quartz-normative tholeiitic basalt, similar in composition to lavas erupted from Kilauea in 1955 and 1962. Plagioclase is the only significant phenocryst; augite, minor olivine, and rare orthopyroxene and opaque oxides accompany it as microphenocrysts. Sulfide globules occur in fresh glass and as inclusions in phenocrysts in early 1977 lavas; their absence in chemically-similar basalt from the later phases of the eruption suggests that more extensive intratelluric degassing occurred as the eruption proceeded. Bulk composition of lavas varied somewhat during the eruption, but the last basalt produced also is differentiated, suggesting that the magma withdrawn from the summit reservoir during the rapid deflation has not yet been erupted. ?? 1980.

Journal of Volcanology and Geothermal Research↗
USGS1976

Earthquakes and related catastrophic events, Island of Hawaii, November 29, 1975: A preliminary report

The largest earthquake in over a century--magnitude 7.2 on the Richter Scale--struck Hawaii the morning of November 29, 1975, at 0448. It was centered about 5 km beneath the Kalapana area on the southeastern coast of the island at 19° 20.1 ' N., long 155° 01.4 ' W.). The earthquake was preceded by numerous foreshocks, the largest of which was a 5.7-magnitude jolt at 0336 the same morning, and was accompanied, or closely followed, by a tsunami seismic sea wave), massive ground movements, hundreds of aftershocks, and a volcanic eruption. The tsunami reached a height of 12.2-14.6 m above sea level on the southeastern coast about 25 km west of the earthquake center, elsewhere generally 8 m or less. The south flank of Kilauea Volcano, which forms the southeastern part of the island, was deformed by dislocations along old and new faults along a 25-km long zone. Downward and seaward fault displacements resulted in widespread subsidence, locally as much as 3.5 m, leaving coconut palms standing in the sea and nearly submerging a small, near-shore island. A brief, small-volume volcanic eruption, triggered by the earthquake and associated ground movements occurred at Kilauea's summit about three-quarters of an hour later. The earthquake, together with the tsunami it generated, locally caused severe property damage in the southeastern part of the island; the tsunami also caused two deaths. Damage from the earthquake and related catastrophic events is estimated by the Hawaii Civil Defense Agency at about $4.1 million. The 1975 Kalapana earthquake and accompanying events represent the latest events in a recurring pattern of behavior for Kilauea. A large earthquake of about the same magnitude, tsunami, subsidence, and eruption occurred at Kilauea in 1868, and a less powerful earthquake and similar related processes are believed to have occurred in 1823. Indeed, the geologic evidence suggests that such events have been repeated many times in Kilauea's past and will continue. The 1975 events serve as a critical, though tragic, reminder of the dynamic nature of the volcano and point up the need for careful land-use planning and adequate building codes to minimize damage and loss of life from similar events in the future. Detailed scientific study of the cause and effects of the November 29, 1975, event will take many months. This report summarizes information available in February 1976.

Hawaii↗
USGS1969

Kilauea Volcano: The 1967-68 summit eruption

On 5 November 1967 Kilauea volcano began erupting lava from vents on the floor of its summit pit crater. Halemaumau, 170 meters deep. This eruption ended nearly 2 years of the quiescence that followed a short lived eruption on the east rift zone of Kilauea in December 1965 (1). The 1967-68 eruption was the first activity in Halemaumau since July 1961 (2). The eruption ceased on 13 July 1968 following 31 separate phases of fountaining separated by short periods of quiescence. Six weeks after the end of the summit eruption, a short eruption occurred on the upper east rift zone of Kilauea. As the article goes to press there have been four eruptions, all of the upper east rift zone. The last of the four began in May 1969 and have just completed its seventh phase. The article summarizes the eruption in Halemanumau and complements an article Fiske and Kinoshita on the deformation that preceded the eruption (3). The methods of study and the instrumentation used during the eruption are the same as those discussed in the earlier article. The locations of all seismographs tiltmeter stations and bench marks are shown in Fig. 1.

Hawaii↗