Paluweh Volcano (Rokatenda / Rerombola Lava Domes)

Paluweh volcano is located about 10km off the north coast of Flores Island, one of the Lesser Sunda Islands in Indonesia. It lies in the Flores-Pantar sector of the Sunda Arc which lies north of the Sunda Trench subduction zone, responsible for volcanism in the area. The sector also includes the active Batu Tara volcano.

Paluweh volcano has formed an island which rises about 3000 meters from the seabed and reaches a height of approximately 900m asl. The diameter of the almost circular island is about 8km. The volcano is largely constructed from a series of lava domes, with the Rokatenda dome being the site of several historical eruptions. The dome was the site of the violent 1928 eruption and has been the focus of activity in subsequent eruptive episodes in 1963, 1972, 1973, 1980-81, 1984 and 1985. Hence, the volcano is often erroneously referred to as Rokatenda. A further poorly vegetated and thus presumably recent dome structure is present in the summit region further west. The new Rerombola dome documented below is forming between these structures.

Two rock samples from Rokatenda gave silicate compositions of 54.87 and 59.88 percent (Wheller et al., 1987. J. Volc. Geotherm. Res. 32, p.137-160), placing it in the basaltic-andesite / andesite range. Samples from the 1928 and 1963 eruptions had silicate compositions of 58 and 62%, respectively, although silicate levels of as low as 48% have been found in samples from the volcano (Newhall and Melson, 1983. J. Volc. Geotherm. Res. 17, p.111-131).

Summit region with degassing Rerombola lava dome	Summit region with Rerombola lava dome

Rokatenda lava dome	Rerombola lava dome (with older structure to left below)

Eruptions threaten the small villages located on the steep flanks of the volcano and the 1928 and 1963 eruptions apparently caused fatalities and property damage. A landslide associated with the 1928 eruption caused a tsunami. The main dangers are however pyroclastic flows resulting from failures of the dome structure. In 1981, 36 buildings were set on fire by a pyroclastic flow. Fortunately, the local population had been evacuated beforehand. In 2013, 5 villagers who had not followed government advice to evacuate the island were killed by a pyroclastic flow.

Overview of historically active area	Village in shadow of volcano	Village in shadow of volcano

Increased seismic activity was reported in April 2009 and again in January 2012. Local resident Ignatius Cua reported that a small zone of dead vegetation associated with new fumarolic activity had developed in the summit region in June 2012 (see image). It appears that lava extrusion commenced at or near this zone in mid-oktober, marking the beginning of the 2012 eruption.

Precursory degassing prior to eruption, June 12, 2012 (Image kindly provided by Ignatius Cua)	2012 Dome as observed on 28.10.2012 (Image kindly provided by Ignatius Cua)

Sustained extrusion in the following weeks has formed a new lava dome, provisionally named Rerombola ("The friendly one") by the locals. The dome rose approx. 150-200m from its base by the time of the visit documented on this webpage (30 Nov.- 2 Dec.). It lies adjacent to the west flank of Rokatenda (and NE of the other poorly vegetated dome structure). It has surpassed Rokatenda in height, thus forming the new summit of the volcano. Several villages in the vicinity of the summit region had been evacuated before our visit and remained deserted. Evacuation is the only effective means of protecting the population from possible pyroclastic flows.

Inactive Rokatenda dome with Rerombola degassing behind	Rerombola lava dome

	Rerombola degassing

Rokatenda (left) and Rerombola (right)	Rerombola degassing at dawn	Rokatenda (left) and Rerombola (right)

During the observation period, activity largely consisted of incandescent rockfalls from numerous sites of extrusion on the upper flanks of the dome. Interestingly, the rocks were relatively robust and tended to cascade down the flanks of the dome often without breaking up significantly. This, combined with what appeared to be a relatively low gas content meant that pyroclastic flows were rare and minor in volume. Interestingly, even the sequential domino-like collapse of two large extrusion lobes with one cascading into the other and detaching it did not result in the generation of a pyroclastic flow. Given that much of the forest at the base of the dome is still intact, it in fact appears that no significant flows have been formed at any stage of dome growth, at least not on the N and E flanks that could be seen from the viewing positions. It is noted that a larger collapse from the dome summit did generate a notable pyroclastic flow to the W which was observed from the fishing boat while leaving the island. This did however again not appear to extend out of the summit region.

	Small pyroclastic flows on flank of Rerombola

Rockfalls / Miniature pyroclastic flows	Rockfalls / Miniature pyroclastic flows

Intense rockfall activity	Rock bouncing down dome	Debris apron with vegetation ignited by glowing blocks

Intense rockfall activity	Larger pyroclastic flow viewed from boat

Sustained weak ash venting (giving a local yellowish-brown hue to the gas rising from the dome) was observed almost permanently from a vent on the N side of the dome summit, whilst a vent on the E side of the dome summit more energetically and audibly produced significant amounts of ash for at least an hour on 2 occasions, resulting in a significant ash cloud above the volcano.

Nighttime ash venting	Nighttime ash venting

Close-up of vent (on left) from nighttime activity shown above	Weak degassing occuring constantly from other vent

View of Rerombola dome at night with incandescent rockfall activity	View of Rerombola dome at night with incandescent rockfall activity

Glowing summit of Rerombola dome	Rerombola at night with minor rockfall	Rerombola at night with minor rockfall

Rerombola at dawn with minor rockfalls	Rockfalls on lava dome in moonlight

Rockfalls on lava dome in moonlight	Incandescence on flank following double lobe collapse

	Extrusion lobes

Extrusion lobes on north flank of Rerombola	Extrusion lobes on north flank of Rerombola

Animation of collapse of extrusion lobe

Since the documented visit, Paluweh has remained active with dome collapse events occuring quite frequently, sometimes associated with pyroclastic flows reaching the sea on the south flank of the volcano. Ash clouds up to 4 km high have been associated with such events on numerous occasions. The fatal partial dome collapse of 10. Aug. 2013, which claimed the lives of 5 people, involved PFs reaching the sea on the north side of the island for the first time.

Humans caught in pyroclastic flows have little chance of survival unless they can reach a protective structure. The impact of pyroclastic flows on humans is discussed in detail in Baxter et al.,1998 (Nat. Haz. 17, p.163-176). Pyroclastic flows are essentially avalanches of hot rocks and volcanic gases containing high ash concentrations. By virtue of their high density, they are thus capable of crushing and sweeping away victims. Even people only caught by the hot ash cloud at the periphery of the flow will suffer severe skin burns, especially to unclothed areas, and will suffer airway obstruction and burning as a result of particle inhalation. Inhalation of large amounts of ash will cause lethal asphyxia even at low temperatures. Inhalation of hot ash, especially in combination with moisture, will additionally lead to rapid heat transfer to the lungs, causing severe damage.

Unfortunately, no english language scientific literature is available on Paluweh volcano. For an understanding of lava domes in general, the reader is referred to the pages on Soufriere Hills, Chaiten and Sinabung volcanoes.

An interesting feature of Paluweh island is that the volcano was effectively the only source of fresh water until regular supplies were established from the mainland. Villagers had learned to tap steam at geothermal sites on the island, channeling it through a series of bamboo pipes where it condenses. Water trickles out of the end of the pipes and is collected.

Collecting water from fumarolic steam emissions	Collecting water from fumarolic steam emissions	View to degassing dome from fumaroles

Visitor Information

Paluweh island is not touristically developed and has no hotels or restaurants. The villagers may however be prepared to host visitors and are very hospitable. Small villages are spread over much of the island and are connected by a network of narrow concrete tracks suitable for travelling by moped. The island can be reached by hiring a fishing boat from the small settlement of Ropa on the N coast of Flores. This is about 2 hours drive W of Maumere.

Leaving Ropa by fishing boat	Landing on Paluweh Island

Before visiting the volcano, local tradition requires that a chicken be sacrificed, cooked and eaten on the slopes leading up the the summit region. The heart is separated and then offered to the volcano to appease it. I chose not to photographically document this ritual as some readers may find it disturbing.

Approaching the lava dome is extremely hazardous as are the surrounding valleys. Dome failures and explosive eruptions can occur with no warning. Sadly, on 10. Aug. 2013, pyroclastic flows killed five villagers sleeping near the coastline in the early hours of the morning. The authorities continue to try and persuade the villagers to leave the island, yet even after this event most wish to stay.

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