Having shivered our way through glaciers and sea ice in the last two posts, today we are moving into warmer climates of the world! With an average temperature of 29°C (82F), an average humidity of 79% and no more than 2 to 5 rainy days per month, this tropical marine climate is just the right place to linger and relax for a while! – Whenever you read the GVP weekly volcano updates, or VAAC ash advisories, you are very likely to see “Pagan” in the list, and you think, oh that one again… But do you really know which one?
Pagan (pronounced ‘pah-gun, means something like “place where it smells” and it has no connection to the other pagan word!) is a small island in the Commonwealth of the Northern Mariana Islands (CNMI), 16km long by 6km at its widest in the northern part. Three volcanic cones constitute the “spooniform” landmass of Pagan, of which the highest, Mount Pagan, is active and produces a constant cloud of steam and ash. The southern Pagan volcano is dormant and connected to the northern part by a narrow, low land bridge down to 700m wide. Pagan is one of the most biologically and geologically diverse islands in the archipelago, and is home to many threatened endemic species. The Chamorro stone ruins skirting her beaches bear evidence that this island has supported the ancestors of Pagan indigenous islanders for over 3,000 years.
North and South Pagan stratovolcanoes were constructed within calderas, 7 and 4 km in diameter, respectively. Mount Pagan at the NE end of the island rises above the flat floor of the northern caldera, which may have formed less than 1000 years ago. South Pagan is a 548-m-high stratovolcano with an elongated summit containing four distinct craters. Almost all of the historical eruptions of Pagan, which date back to the 17th century, have originated from North Pagan volcano. The largest eruption of Pagan during historical time took place in 1981 and prompted the evacuation of the sparsely populated island.
A roughly circular caldera, with a prominent southern wall and more subdued, partly buried northern and eastern scarps includes more than half of the subaerial part of Mount Pagan. Preliminary calculations of the volume of the volcanic edifice that occupied the remnant caldera are ~4.7 to 5.8 km^3. This implies that the caldera-forming eruption was large and, at least, a VEI 5. Mount Pagan itself rises to an elevation of 570m near the center of the caldera. On the western flank of Mount Pagan is a roughly 2×2-km depression with a lake in its floor. The deposits surrounding the depression are characteristic of phreatomagmatic eruptions, so this feature is interpreted as a maar.
Radiocarbon data of a 10,000-year-old lava flow suggest that most of the stratigraphic succession above it, including the presumed caldera-forming unit, is of Holocene age. Most of the new age measurements suggest that Mount Pagan has erupted frequently and grown rapidly since the caldera formation, probably less than 1,000 years ago. The RC measurement unit called Qbap15 overlies a basaltic andesite flow on the north caldera wall and adjoining sea cliff that has a radiocarbon age of 235 ± 35 years B.P., indicating that the Mount Pagan caldera is very young and possibly historic in age. Hence, it must be regarded as a potentially dangerous volcano.
Pagan Island is the subaerial portion of two adjoining Quaternary stratovolcanoes near the middle of the active Mariana Arc. It belongs to the Izu-Bonin-Mariana (IBM) arc system which is an outstanding example of a plate tectonic convergent boundary. IBM extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, Bonin Islands, and Mariana Islands; much more of the IBM arc system is submerged below sea level. The IBM arc system lies along the eastern margin of the Philippine Sea Plate in the Western Pacific Ocean. It is most famous for being the site of the deepest gash in Earth’s solid surface, the Challenger Deep in the Mariana Trench, north of Saipan.
Pagan and the other volcanic islands that constitute part of the Arc form the northern half of the East Mariana Ridge. The ~11-km-deep Mariana Trench adjoins the East Mariana Ridge on the east, and the Mariana Trough, partly filled with young lava flows and volcaniclastic sediment, lies on the west of the Northern Mariana Islands. The volcanic islands that comprise these island arcs are thought to have been formed from the release of volatiles (steam from trapped water, and other gases) being released from the subducted plate, as it reached sufficient depth for the temperature to cause release of these materials. The associated trenches are formed as the oldest (most western) part of the Pacific plate crust increases in density with age, and because of this process finally reaches its lowest point just as it subducts under the crust to the west of it.
Beneath the Northern Mariana Islands, earthquake hypocenters at depths of 50-250 km identify the location of the west-dipping subduction zone, which farther west becomes nearly vertical and extends to 700 km depth. During the past century, more than 40 earthquakes of M 6.5 to 8.1 have shaken the Mariana Trench.
The Mariana Islands form two sub-parallel, concentric, concave-west arcs. The southern islands comprise the outer arc and extend north from Guam to Farallon de Medinilla. They consist of Eocene to Miocene volcanic rocks and uplifted Tertiary and Quaternary limestone. The nine northern islands extend from Anatahan to Farallon de Pajaros and form part of the inner arc. The active inner arc extends south from Anatahan, where volcanoes, some of which are active, form seamounts west of the older outer arc. Other volcanic seamounts of the active arc surmount the East Mariana Ridge in the vicinity of Anatahan and Sarigan and north and south of Farallon de Pajaros. Six volcanoes (Farallon de Pajaros, Asuncion, Agrigan, Mount Pagan, Guguan, and Anatahan) in the northern islands have erupted during the past century, and Ruby Seamount erupted in 1996.
HISTORIC ERUPTIONS & MONITORING
Despite centuries of settlement, few detailed studies have been made of the geology and historic eruptive activity of Mt. Pagan. A few eruptions were reported as early as the 1600s; a large eruption was reported in 1872–73, and relatively minor activity was noted during the 1920s. Only after the United States annexed the Marianas in the aftermath of World War II, Corwin and others (1957) assessed the geology of Pagan Island and constructed a geologic map distinguishing different rock types, like tuff, clinker ‘a‘a, pahoehoe, and cinders, but partly on the basis of their suitability as construction materials.
1981 to 1985: A major explosive eruption occurred in the larger of the two historic eruptive centers on Pagan Island. The eruption was preceded by an increase of locally felt earthquakes in late March or early April 1981 and by new ground cracks, new sublimates, and increased gas emissions. On 15 May, closely following a loud sonic boom, a strong Plinian column issued from the volcano. Communication was then cut off. An infrared image from the GMS showed a very bright circular cloud about 80 km in diameter over the volcano. The high-altitude ash cloud (~13.5 km) travelled SSE, but ash and scoria deposits were thickest (>2 m) in the NW sector of the island because of the prevailing low-altitude southeasterly winds. Ashfall was also reported from Agrigan Island, 105 km NW. The USN reported that aircraft crews saw lava flowing down the NE and NW flanks toward the sea, and down the SW flank towards the village and local airstrip.
The Japanese merchant ship Hoyo Maru rescued all 53 persons on Pagan Island early on 16 May – little did they know that they were never to return home… Only one minor injury was reported, but some livestock were killed outright, and others were starving because of extensive destruction of vegetation. The eruption did not cause serious chemical hazards in the local water supply. A flight survey on 17 May showed that the SW flank flow had partially covered the airstrip, but had stopped before reaching Shomushon village, 4 km from the summit.
This eruption (probably) began along a fissure system as a magmatic event but 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 consisted almost entirely of juvenile material. Lithic blocks and juvenile bombs as large as 1m in diameter were thrown more than 2km from the summit, and evidence for base-surges was observed on the N and S slopes of the volcano. The central vent was in a notch about 100 m deep in the N rim of the old summit crater. This vent probably ejected most of the material in the large eruption cloud, and it fed flows that went N, NNE, and W. The third and southernmost vent was in a notch about 80 m deep in the S rim of the old summit. This vent fed the flows that moved S.
The 15 May lava is predominantly of a’a’ type and ranges from 3m to >30m thickness. In composition, it is a high-alumina basalt with small (<1mm long) phenocrysts of plagioclase and clinopyroxene (7%) which is fairly typical in basalts of the northern Marianas volcanoes. It contains slightly more SiO2 (52%), K2O, TiO2, and less Al2O3 and CaO than does the basalt of the previous 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.
The activity of the volcano remained high. Seismic monitoring 20-28 May showed continuous harmonic tremor indicating movement of magma a few kilometers beneath the surface, and short bursts of high-frequency signals, indicating intermittent extrusive events such as degassing and low-level lava fountaining. The ongoing harmonic tremor suggested that more secondary eruptive activity may take place. At the same time, no significant earthquake activity was detected, indicating no prominent build-up of stresses typically associated with activities prior to a major explosive eruption. However, the deformation survey indicated possible swelling of the volcano, which may lead to an increase in future microearthquake activity and eventually to a more significant eruptive event.
Overflights of Pagan by the USN in July and the USGS in September revealed the formation of a new crater, 60-80m in diameter, in the center of the old summit crater. Fume emission rates from the new vent appeared to be significantly greater than the combined rate observed in late May. For some of the eruptions, precursory seismicity and possibly deformation occurred. 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.
A note in the Febr. 1982 report says: The 53 residents of Pagan, evacuated during the second day of the 1981 eruption, have not yet been able to return for more than brief visits to the island. As we know now, this was going to be permanent, because in the following years Shomushon village has been mostly destroyed by flooding and debris flows after that 1981 eruption.
In March 1983, measurements showed that 25 cm of net inflation had occurred on the higher slopes of the volcano since May 1981, but the lack of other measurements between those dates prevented determination of shorter-term deformation trends. Stratigraphy of the tephra deposits indicated that Pagan had erupted at least four and perhaps as many as seven times since May 1981. This relatively high activity period lasted untill about 1985.
1986 to present: As far as was reported by occasional visitors or passers-by, and gleaned from satellite imagery, the volcano has been moderately active during the last 29 years.
NASA’s Earth Observatory noted in 2012 that, for three years, North Pagan had emitted intermittent volcanic plumes. By mid-2011, Pagan’s activity was nearly continuous, and NASA’s MODIS instrument detected a plume almost every time there was a clear view. However, all eruptions were of weak to moderate strength
GVP’s most recent report on Mt. Pagan volcano dates from 18 June-24 June 2014:
Low-level unrest continued at Pagan during the week of 20 June; seismicity remained above background levels. A steam-and-gas plume was visible in web camera and clear satellite images. The Aviation Color Code remained at Yellow and the Volcano Alert Level remained at Advisory.
USGS’ latest report from Oct. 30, 2015 states: Seismic, infrasound, and web camera data from Pagan Volcano remain temporarily unavailable. Nothing unusual observed in satellite images over the past week. Volcanic gas from Pagan may be noticed downwind of the volcano as a distinctive sulfurous odor. […] Access to the island may be restricted by the CNMI government. Contact the EMO for the latest information.
In reports after the 1981 eruption some equipment as tiltmeters and seismometers were mentioned, yet it was never stated that, and when, they had ceased working. So we find in
– 2009: “The U.S. Geological Survey (USGS) does not currently have monitoring instruments on Pagan. Monitoring is by satellite and ground observers”.
– 2010: “Pagan is not monitored with ground-based geophysical instrumentation. The only sources of information are satellite images and occasional reports from observers who pass or visit the island”.
– 2013: First mention of a seismic network and webcameras which had probably been installed by a field crew in June of that year: “The seismic network at Pagan recorded tremor and small discrete earthquakes during 9-16 August, indicating low-level unrest. A steam-and-gas plume was visible in satellite images during periods of clear weather and from web-camera images. A small explosion with a relatively high amplitude seismic component and small infrasound component occurred on 12 August”.
– 2014: The last webcamera image, still there for everyone to see, dates from 18 August. R.I.P.
– 2015: October 23, Seismic, infrasound, and web camera data from Pagan Volcano remain temporarily unavailable. Storm activity obscured satellite images for most of the past week.
A mischievous mind could think that monitoring of Mt. Pagan might well be available (now that the US Military is planning to get comfy over there) – but not to the public! And that we never will see a webcam picture of it again if their dreams come true… (scroll down for the story)
Pagan has the Chamorro Time Zone (formerly the Guam Time Zone, for Guam and the Northern Mariana Islands), UTC+10:00h. – The Chamorro are the indigenous peoples of the Mariana Islands. They were expert seafarers and skilled craftspeople. The latte, a megalithic rock pillar topped with a hemispherical capstone, was used by early Chamorros as foundation for buildings and has since been appropriated as a “national” symbol.
Pagan Island, as many of the other Islands of the CNMI, has always been a playground for the rich and powerful, beginning with the discovery of the islands by a deserter of the Spanish Magellan expedition in 1521. Spain, and later Germany, had their hands on it to exploit natural resources (Copra and Cocos).
More recently, Japan occupied Pagan during WW2, settling some 2000 soldiers and making the indigenous Chamorro population work in pozzolan mines (pozzolan is added to cement to produce hydraulic cement, which is capable of hardening underwater). In 1934 the occurrence of almost pure sulfur (93% S, 7% Cristobalite, Quartz and Alunite) was discovered in lense-shaped deposits of ~60cm diameter, just below the surface, and consequently mined.
Towards the end of WW2, Pagan Island suffered horrendous wall-to-wall bombing by the US forces, leaving it to this day pockmarked with bomb craters and littered with rotting remains of war equipment. After the surrender of the Japanese garrison in 1945, the US administered the Northern Mariana Islands. In the 1950s, parts of Pagan became a copra farm again and a cattle ranch, of which efforts were abandoned in the 1970s. In 1981, the eruption of Mount Pagan forced the remaining local population to relocate to Saipan. Since that eruption, Pagan has remained largely uninhabited; largely meaning that there are still people living temporarily or permanent on the island: Currently, residents can return to Pagan on the condition that they have a plan to get there, have 24/7 communication available and be able to evacuate upon notice. A newspaper article from Jan. 2015 stated that 8 people were living permanently on Pagan (in a visitor’s blog it was mentioned that these even get internet service). Feral cattle and pigs, descendants of the animals that were left behind 1981, are now roaming the island.
Plans by a Japanese investor group to use Pagan as a dumping ground for debris and rubble from the 2011 Tohoku earthquake and tsunami in Japan were provisionally shelved after protests in June 2012. The CNMI is a small land-limited island nation. In this view, turning one of their most biologically diverse islands into a permanent garbage dump for a wealthy country certainly was an ill-fated and atrocious act.
Now the U.S. Military plans to occupy ALL of Pagan Island for live-fire training and military exercises (which could include anything from artillery to bombing, chemical warfare etc.), ignoring the indigenous rights of Pagan Islanders, and the devastating environmental impacts that such activity would cause. Not only will the arable patches of topsoil become unusable and eco-tourism impossible, but Pagan’s coral reefs and its unique flora and fauna are undoubtedly at the risk of destruction. These disturbances, combined with the unexploded devices and toxins that are sure to be left behind, will render this island uninhabitable for centuries to come. To the Chamorro and Refaluwasch people, the impact of destroying Pagan is like the heartache most Americans would suffer from the destruction of Yosemite National Park. The US has 3.79 million square miles of land. The CNMI only has 177 square miles. Of this, the US Military already controls 30.4 square miles. This is in addition to the land they have taken on Guam, which is 1/3 of that entire island. The needless, terrible waste of one of the most beautiful places in the world should be stopped! I don’t know the present state of affairs, but if you feel you want to help some way, please refer to those websites that protest against the destruction of Pagan Island by the U.S. Military. Two of them here and here. Also, you may want to read this comment and other discussions.
Enjoy! – GRANYIA
SOURCES & FURTHER READING
– Pagan on the GVP
– The eruption of Mount Pagan volcano, Mariana Islands, 15 May 1981 (Abstract, 1984)
– Geochemistry of Southern Pagan Island Lavas… (2012, PDF)
– Save Pagan Island (Blog)
– Preliminary Geologic Map of Mount Pagan Volcano… (2006, PDF)
– USGS volcano information
– USGS reports on Pagan volcano activity
– 2 webcams (down since 2014)
– Stars and Stripes (News)
– Pagan, Northern Marianas (by Dr. B. Lorenz, 1999)
– Huffington Post (News)
– LA Times (News)
– Suuhaa: Ocean Run (Blog)