Bromo Volcano (Tengger Caldera)

Mount Bromo (2392m) is a small pyroclastic cone which rises 133m above the surrounding floor of the massive (9x10km) Tengger Caldera. This caldera, also referred to as the sand-sea caldera due to its flat sandy floor, is the result of the collapse of the top half of a probably nearly 4500m high pre-caldera stratovolcano over 250000 years ago. Bromo has been frequently active since historical records began in 1804, with a total of over 50 eruptions being recorded up to the present date. Due to its location on the base of a steep-walled caldera, it generally only poses a local threat to life during explosive eruptions. These may occur with little warning. Such an eruption occurred on 08.06.2004 and accounted for 2 fatalities in the vicinity of the crater due to the impact of ballistics. Damage to vegetation may occur over a much wider radius, as could be witnessed during e.g. the 2010-2011 eruptive phase.

Post-caldera vents of Tengger Caldera - Batok in center, Bromo to its left. Semeru smoking in background (2004)	Strombolian activity in Bromo Crater, 2011

Bromo erupting in 2011	Bromo erupting in 2011	Bromo erupting in 2011 - Batok cone to right

Basic Geology and Eruptive History

Several phases can be defined in the evolution of the Tengger Caldera volcanic complex (summarized in Gerven and Pichler, 1995. J. Southeast Asian Earth Sci. 11(2), p.125-133). The original Tengger stratovolcano was built up by a succession of pyroclastic deposits and lava flows to a height of about 4500m. This would make it the highest mountain in Java in the present day. A further slightly smaller volcano, Ngadisari, adjoined it in the NE side. Ngadisari collapsed after a massive eruption around 150000 years ago, forming a caldera. At a later time, eruptions from vents in the Ngadisiri Caldera resulted in the emplacement of significant amounts of ignimbrites (pyroclastic flow deposits) and also some lava flows. The products of these eruptions built up what is now the NE wall of the Tengger caldera, also referred to as Cemoro Lawang. The Tengger Caldera itself formed over 45000 years ago following what must have been a huge eruption, possibly similar in magnitude to that of Krakatau in 1883. The final stage of activity has involved the emplacement of 6 intra-caldera vents.

	1. Segarawedi Kidul (2661m) 2. Segarawedi Lor (I and II) (2650m) 3. Mount Kursi (2581m) 4. Mount Bromo (2392m) 5. Mount Batok (2470m)
Fig.1 Sketch Map of Tengger (Sand Sea) Caldera

The six vents created by the Post-Caldera phase of activity are numbered in order of appearance in Fig.1. These mainly consist of ash fall and lapilli units, with only the eruption of Segarawedi Kidul being associated with the emplacement of pyroclastic flow units. Batok appears to be the youngest, yet only Bromo is presently active.

Numerous eruptions of Bromo have now been documented. Recent activity appears to have been largely phreatic, involving water that accumulates in porous pyroclastic material in the caldera as a result of the high amount of rainfall experienced in the area. This has led to the eruption of ash, lapilli and, in the more powerful stages of the eruptions, volcanic bombs. The eruptions are difficult to predict, although Abidin et al., 2004 (J. Glob. Pos. Sys. 3(1-2), p.16-24) show that the volcano inflates gradually by a few cm pre-eruption and deflates rapidly afterwards. This fluctuation could be detected by GPS surveying methodology. The pressure source appears to lie in the center of the post-caldera unit. Tremor and shock sources under Bromo have also been studied during a phase of high activity in 1995 (Gottschämmer and Surono, 2000. J. Volc. Geotherm. Res. 101, p.199-209). Both sources were found to be located under the NW part of Bromo in the vicinity of the then active vent. The authors concluded that the tremor signals were largely due to flow of gases and steam through an irregularly shaped conduit. The shock signals were attributed to fissuring of the conduit wall due to the high pressure inside. As of 2011, the regular monitoring network remains rudimentary with only a single seismometer in place. Hence, no inflation data is generally available, nor is it possible to localize tremors.

Activity at Bromo has taken on different forms in historic times and Bromo apparently contained a lava lake from 1836-1841 and again briefly in 1842. From its beginnings, activity at the Tengger Caldera has been dominated by eruption of basaltic to andesitic rocks. The basaltic rocks are mainly found in lava flows from the pre-caldera phase of activity. All recent lava flows of the post-caldera unit are andesitic in nature, as are most of the recent eruptates of Bromo (van Gerven and Pichler, 1995).

Historical activity at Bromo is usually short-lived, generally lasting for three months or less, with the major events taking place over a shorter period. The eruptions usually involve weak explosive activity (V.E.I 1) and periods of steam and ash venting. However, slightly more powerful eruptions have been witnessed in 1915-1916 and 1948, reaching an explosivity index of 3. These apparently led to property damage by direct impact of ballistics.

2010-2011 Eruptive Phase

An increase in volcanic tremor was detected at Bromo at the beginning of November 2010. By the 22nd, tremor was almost continuous and increased degassing was evident, leading authorities to raise the alert level to 4 on the 23rd. First significant ash emissions were noted on 26 Nov. marking the onset of the eruption. Output of ash was high at several stages in the eruption and led to significnt damage to vegetation in downwind areas. Flights have been disrupted at nearby Malang City airport, but also as far away (400km) as Bali, where numerous flights were cancelled on 28.01.11 when an up to 5500m high ash cloud extended from Bromo to the island.

Activity in mid-March 2011 as documented below could be distinguished into largely strombolian phases accompanied by little ash and variable levels of degassing, and phases during which significant amounts of ash were released. Strombolian phases were sometimes accompanied by powerful shockwaves, often after short periods (10-30 secs) of complete calm, presumably signifying blockage of the vent resulting in pressure buildup.

Ash-rich phase starting approx. 05:30 local (19.03.2011):

Ash-rich phase starting approx. 09:45 local (22.03.2011):

Visit to crater rim, 20-21 March 2011:

Bromo crater during pause in activity	Walking along east rim of Segarawedi Lor, approaching Bromo	Vent during pause in activity

	Strombolian eruptions of Bromo at night

	Strombolian eruptions of Bromo at night

Degassing	Ash eruption	Ash eruption

Minor emission of gas with traces of ash	Ash eruption	Weak strombolian activity accompanied by strong degassing

Descending East Flank (March 21, 2011):

View to rim from east flank	Large lava bomb on flank

Trails on flank mark path of bombs	Trail left by bomb in barren landscape	Small bomb at end of trail

	Forest on flank killed by heavy ashfall

Large bush completely smothered by ash	Ash on flank	Extensive ash deposits, Batok in background

View from Batok Cone:

Building buried by ash at base of Batok	Moisture condensing in cloud above crater	View from Batok with dead vegetation in foreground

View from Batok with dead vegetation in foreground	Minor ash eruption

Temple at base of Bromo / Batok:

The Pura Luhur Poten temple at the base of Bromo is a Buddist / Hindu temple holy to the Tenggerese community. During the annual Yadnya Kasada ceremony (see section at bottom of page), offerings of food are thrown into the crater of Bromo volcano, activity permitting.

Pura Luhur Poten temple in foreground with erupting Bromo behind	Pura Luhur Poten temple

Pura Luhur Poten temple with ash cloud passing overhead	Pura Luhur Poten temple viewed from trail up Batok

View of Eruptions from near Temple:

Impact of ash fall:

Footprint in fresh ash	Fern coated in ash	Plant buried in ash

Dead forest on east flank of Bromo	Plant smothered by ash	Locals clear trees broken by ash from road into caldera

Agricultural land smothered in ash, 10km SSE of Bromo	Trees snapped by weight of ash in caldera	Crops bent and broken by ash fall

Short-Lived Eruption in 2004

The 08.06.04 eruption also shows that Bromo can be dangerous, especially as it is frequently climbed by tourists and eruptions can come without warning. In 2004, the main eruptive event came without any obvious precursor and caught a number of tourists by surprise as they were on the staircase leading up to the crater. Two tourists were killed by direct impact of ballistics and several more injured. A several kilometer high eruption column was produced during the main event which lasted less than 2 hours. Minor ash emissions were reported for several days before the volcano returned to dormancy, The photos in this section were taken weeks after this eruption and show the amount of ballistics that were thrown from the crater during the eruption and some of the damage they caused. High concentrations of volcanic gases in the crater (especially Hydrogen Sulphide) may also pose a danger, and have accounted for fatalities in the past according to van Gerven and Pichler (1995).

View into Bromo Crater, July 2004	View into Bromo Crater, July 2004	View into Bromo Crater, July 2004

Building on Flank of Bromo with Roof Destroyed by 2004 Eruption	Vegetation Damaged by Impact of Bombs from 2004 Eruption	Fresh Lapilli from 2004 Eruption by Staircase

Volcanic Bomb from 2004 Eruption (Banknote for Scale)	Volcanic Bomb from 2004 Eruption	Ash Deposits on Flank of Bromo

Morning View from Mt. Penanjakan Viewpoint	Expansive Morning View from Mt. Penanjakan Viewpoint

Erosion Valleys on N Flank of Bromo	Evening View of Bromo from Batok

View from Bromo Flank to Batok	Multiple Small Impact Craters from 2004 Eruption (Located in Foreground of Picture to Left)	View from Base of Caldera to Bromo. Note Impact Damage to Roof of Toilet

Hindu Yadnya Kasada Ceremony (August 2011)

The climax of the month-long annual ceremony is held in the early hours of the morning on the full moon around the 14th day of the month of Kasodo, as defined by the Tenggerese Calendar. The ceremony involves a procession from the rim of the Tengger Caldera to the Pura Luhur Poten temple near the base of Bromo volcano. Torch-bearers and a small band accompany the bearers of sacrificial "wreaths" and priests as the procession makes its way through the usually fog-filled sand-sea caldera floor, occasionally halting at small altars along its path. After reaching the Pura Luhur Poten temple, ceremonial proceedings are initiated, involving music, meditation and speeches from several of the priests. After this, sacrificial wreaths and bundles, largely consisting of agrigultural produce, are carried to the rim of Mt Bromo to be thrown into the crater. This usually occurs before sunrise, yet local people continue to perform their own sacrifices in the following hours as large crowds ascend the staircase to the crater rim. Most of the sacrificial goods are retrieved by poor people standing below the rim in the crater, some armed with nets for catching the smaller offerings. Even though this prevents the volcano from actually receiving the sacrificial goods, it appears that this is an accepted part of the ceremony.

Priests performing ceremony before procession	Procession through dense fog on caldera floor	Musicians accompanying procession

Priests meditating in Pura Luhur Poten temple	Musical accompaniment of ceremony	Pilgrims keep warm by fire in temple compound

Priest holding speech in Pura Luhur Poten temple	Sacrificial “wreath” being carried up stairs to Bromo crater

Sacrificial “wreath” being thrown into Bromo crater	Bundle of agricultural produce for throwing into crater	Priest with sacrificial “wreaths” on crater rim

Waiting to catch sacrificial goods in crater	Sacrificial goat being retrieved from crater	Pilgrims and onlookers ascending stairs to crater rim

Pura Luhur Poten temple	Pura Luhur Poten temple with Bromo Volcano behind	Pura Luhur Poten temple with Bromo Volcano behind

According to local legend, in the 15th Century, Roro Anteng and her husband Jaka Seger (first royal leaders of the Tenggerese offshoot of the Majapahit Kingdom) climbed Mount Bromo volcano to address the god residing therein in the hope of overcoming their inability to produce offspring. The god of Mt. Bromo assured them offspring, albeit under the condition that the youngest offspring be sacrificed by throwing it into the crater of the volcano. After having 25 children, the couple needed to fulfil their part of the deal. Initially hesitant, the increasing wrath of the volcano god (presumably in the form of increased activity) persuaded the couple to perform the sacrifice of their child, named Kasuma. The ceremony commemorates this act and also serves as a main focus for the about 600000 people in the region adhering to the local Hinduistic traditions and speaking the Tengger dialect.

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Whilst most visits to Bromo occur without incident, those wishing to avoid any risk may look over the Tengger Caldera from the highly frequented viewpoint on Mt. Penanjakan (2770m) which represents a highpoint on the northern rim of the caldera. The viewpoint is particularly popular at sunrise and provides expansive views of the caldera with nearby Semeru volcano in the background. Accommodation is available in the village on the East rim of the caldera.

When the volcano is not active, tourists may climb a path to its rim, starting from the vicinity of the temple. A staircase has been built into the upper flank for this purpose. A rough and steep path also leads up the eastern side of Batok cone and provides a good overview of Bromo. Jeeps, mopeds and horses are available to transport tourists from the village to the temple.

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