Tag Archives: stratovolcano

Indonesia

Gunung Merapi, Alert Level 3, Aviation Code Orange

Good afternoon!

Today we are taking a trip to Java, Indonesia, away from the gentle effusive eruption at Fagradalsfjall, Iceland, and what looks like the growth of a shield volcano, to the more explosive activity at the subduction zone between the Indo-Australian Plate and the Sunda Plate, focussing on Gunung Merapi. 

Merapi has been erupting since the start of the year, with the growth of two lava domes, block and ash falls and pyroclastic flows generated from partial collapses of the lave domes.  The current alert level is 3 (Siaga) and the aviation code is orange.  (Siaga translates as, using Google Translate, “Stand By” (There was a significant increase in volcanic activity. Eruption is most likely to occur and the area of potential eruption hazard is in the area of ​​Disaster-Prone Areas (KRB) II. The community is prohibited from carrying out activities in the KRB II area). The exclusion zone extends 5km from the summit).

Fig 1:  Merapi 2011 with Prambanan in the foreground, cropped from an image of Prambanan by Arabsalam, published under CC BY-SA 4.0.  Source: Prambanan Java243.  Prambanan is an 8th Century Hindu temple compound located approximately 17 kilometres (11 mi) northeast of the city of Yogyakarta and designated a UNECSO World Heritage Site.

Background

Merapi is a 2,968 m high stratovolcano located 25 km north of the city of Yogyakarta on the island of Java, Indonesia.  Volcanic activity at Merapi is believed to have started around 170,000 years ago.  Since then, activity alternated between effusive and explosive, the latter with lava domes and pyroclastic flows.  While her eruptions are comparatively modest (VEI 1 to 4), her proximity to a large metropolis means she has the potential to do a lot of damage, hence her status as a Decade Volcano. Over 4 million people live within 30 km of the volcano and over 24 million people live within 100 km of the volcano.

Yogyakarta, itself, is a densely populated city in the Special Region of Yogyakarta.  373,589 people live in the city (Census 2020) and over 4 million in the metropolitan area.  It is a sophisticated centre for Javanese fine arts, culture and education.  Yogyakarta has been home to the seat of power for the Medang Kingdom between the 8th and 10th century and Mataram Sultanate between 1587 and 1755.  Explosive eruptions from Merapi, which destroyed many Buddhist and Hindu temples built between 732 AD and 900 AD (and presumably caused other significant damage), may have been a factor in the migration of the Mataram Kingdom to East Java in 928 AD or 929 AD.

Tectonic Setting

Volcanic activity on Java is driven by the northward subduction of the Australian Plate under the Sunda Plate at the Sunda Trench.   The western, southern and eastern boundaries of the Sunda Plate are tectonically very active. 

We downloaded earthquake data from EMSC for the period October 2004 to July 2021 between 14.04°S 86.16°E to 12.66°N 127.48°E to take a look. This area is larger than the area under discussion to make sure that subduction zone was captured.  The following images are from extracts of that data.

Fig 2: Subduction zone at the Java Trench section of the Sunda Trench.  Dots denote earthquakes, blue triangles, volcanoes.  The orange triangle is Merapi.  © Copyright remains with the author; all rights reserved, 2021.
Fig 3:  Tectonic setting – plot of earthquakes between October 2004 and July 2021 by the author.  Earthquakes clearly delineate the plate boundaries. Green dots denote earthquakes below 6.0 M, yellow dots, earthquakes between 6.0 M and 7.0 M, red dots, earthquakes between 7.0 M and 8.0 M, silver stars, earthquakes between 8.0 M and 9.0 M and orange star, earthquakes over 9.0 M.  Blue triangles denote volcanoes.  The orange triangle is Merapi.  © Copyright remains with the author; all rights reserved, 2021.

Merapi is located at the intersection of two volcanic lineaments:  the north – south trending Ungaran-Telomoyo-Merbabu-Merapi; and the east – west trending Lawu – Merapi – Sumbing – Sindoro – Slamet.  Ungaran-Telomoyo-Merbabu-Merapi is a double chain volcanic arc, with Ungaran as the back arc and Telomoyo-Merbabu-Merapi as the trench side volcanoes. Merapi is also bounded by two faults: the north – south Merapi – Merbabu fault and the Baribis – Semarang – Kendeng fault.  

Fig 4:  Earthquakes in Java from October 2004 to July 2021 plotted by the author.  Red and grey lines denote approximate locations of major faults, blue lines, volcanic lineaments, blue triangles, volcanoes and orange triangle, Merapi, black rectangle on the left is the area plotted.  © Copyright remains with the author; all rights reserved, 2021.

Growth of Gunung Merapi

Merapi formed in the late Pleistocene and Holocene in three stages: Proto-Merapi, Old Merapi and New Merapi.

Proto-Merapi emerged after 170 ka and includes Gunung Bibi, dated to 190 ± 60 ka, Gunung Turgo, 138 ± 3 ka, and Gunung Plawangan ,135 ± 3 ka.

Gunung Plawangan was home to a volcano observatory until the 1990s but was abandoned due to nuée ardentes from the current cone.

The summit of Gunung Turgo is home to sacred graves including that of Sheikh Jumadil Qubro, a direct descendant of the Islamic prophet, Muhammad.

Old Merapi started to grow around 30 ka, reaching a height slightly more than the current cone; growth ended with flank failures 4.8 ± 1.5 ka.  Collapse of the caldera with debris avalanche flows to the south and west left a Somma rim on the eastern slope. 

Gunung Batulawang and Gunung Kendil are part of Somma – Merapi. Gunung Batulawang is the highest peak of Old Merapi.  Lake Borobudur formed c 3,400 14C years BP. 

The latest Somma collapse was around 1,900 14C years BP. 

New Merapi, the current cone, grew soon after the growth of Old Merapi ended.  Partial edifice collapse of New Merapi may have occurred 1,130 ± 50 14C years BP. 

Gunung Selokopo Ngisor, Gunung Pusunglondon, Gunung Patukalapalap, Gunung Dengkeng, Gungung Selokopo Duwur and Gunung Gadjah Mungkur are hills which are thought to belong to New Merapi.

Volcanic Activity

Merapi’s lavas are typical for a subduction zone, being andesite / basaltic andesite, trachyandesite, basaltic trachyandesite with some basalt / picro basalt and trachybasalt / tephrite basanite.  Her lavas have evolved over time. Her early lavas were effusive basaltic.  The K2O content of the lava has increased over time; Old Merapi had lower K2O lavas than New Merapi and nearby Gunung Telomoyo and Gunung Merbabu. 

According to GVP, there have been 111 Holocene eruptions, ranging from VEI 1 to 4.  The most recent eruption, currently a VEI 1, started on 31 December 2020, with new lava domes extruded in January and February 2021, and, at the time of writing is ongoing.  The most recent VEI 4 was the devastating October 2010 to July 2012 eruption in which partial dome collapse caused pyroclastic flows that destroyed villages, led to the evacuation of more than 300,000 people and caused 386 fatalities; the ash plume reached 18km between 4-6 November; and, the largest pyroclastic flows occurred on 26 October 2010 and 5 November 2010 – the latter produced the widest pyroclastic flow seen in Indonesia for 100 years.  By mid-November, eruptive activity subsided, to be followed by lahars as the main hazard.

The 26 October eruption started 19 hours after tsunamis caused by earthquakes on the Sunda Trench swept away villages on the Mentawai Islands, killing 428 people and displacing thousands. The earthquakes were a 7.7 M, preceded by a 5.8 M and followed by aftershocks that included a 6.1 M and 6.2 M.  Whether or not the earthquakes triggered the eruption, itself, is open to debate; the volcano was ready to erupt. Since 2007 swarms of volcanic earthquakes had been occurring; deformation and gas emissions increased in September 2010; and, seismicity increased between 15 – 26 October, ramping up during 20 – 26 October.  The alert levels were raised to level 2 on 20 September 2010, level 3 on 21 October 2020 and level 4 on 25 October 2020.

A phreatic eruption on 11 May 2018, heralded a new phase of lava dome growth. In November 2020, evacuations were ordered due to decreasing stability of the lava dome. Eruptions commenced on 4 January 2021, leading to further evacuations in the Yogyakarta region.

Here’s hoping the current eruption remains a VEI 1.

The Armchair Volcanologist

©Copyright remains with the author; all rights reserved, 2021.

Sources and Further Reading:

Raw earthquake data, EMSC: https://www.emsc-csem.org/Earthquake/info.php

The Smithsonian Institution’s Global Volcanism Program (GVP): Merapi

Ralf Gertisser, Silvain J. Charbonnier, Jörg Keller, Xavier Quidelleur, “The geological evolution of Merapi volcano, Central Java, Indonesia”, Bulletin of Volcanology (2012) 74: 1213=1233. DOI: 10.1007/s00445-012-0591-3

Newhall, C. G., Bronto, S., Alloway, B., Banks, N. G., Bahar, I., del Marmol, M. A., Hadisantono, R. D., Holcomb, R. T., McGeehin, J., Miksic, J. N., Rubin, M., Sayudi, S. D., Sukhyar, R., Andreastuti, S., Tilling, R. I., Torley, R., Trimble, D., Wirakusumah, A. D., “10,000 Years of explosive eruptions of Merapi Volcano, Central Java: archaeological and modern implications”, Journal of Volcanology and Geothermal Research 100 (2000) 9 – 50. DOI:10.1016/S0377-0273(00)00132-3

Wikipedia:

Mount Merapi: Mount Merapi – Wikipedia

Yogyakarta: Yogyakarta – Wikipedia

Africa, East African Rift System, Plate Tectonics

Eruption of Mount Nyiragongo, Democratic Republic of the Congo, 22 May 2021

Good Afternoon!

The recent eruption Mount Nyiragongo has taken us away from Iceland and the ongoing eruption at Geldingadalur, Fagradalsfjall, Iceland, to look at the East African Rift System. Unlike the current benign eruption in Iceland, there are 32 known fatalities from Mount Nyiragongo’s eruption, 3,629 homes and buildings destroyed, more than 20,000 displaced, many unaccounted for and several hundred thousand evacuated from parts of Goma to Sake.  The current alert status for the volcano is orange.  Our thoughts are with all those affected by the eruption.

As we refer to different lavas in more detail than originally anticipated, we will explain them in future posts; please bear with us for the moment.

Fig 1: Photo of Mount Nyiragongo by B. Martinelli, 1994 (courtesy of Jack Lockwood, U.S. Geological Survey) (left) and screenshot of the Nyiragongo crater with lava lake pre 2021 eruption from Google Maps (right).
Fig 1: Photo of Mount Nyiragongo by B. Martinelli, 1994 (courtesy of Jack Lockwood, U.S. Geological Survey) (left) and screenshot of the Nyiragongo crater with lava lake pre 2021 eruption from Google Maps (right).

It has been reported that the volcano had not been fully monitored for several months due to lack of funding for the Goma Volcano Observatory. Monitoring improved in May 2021 when an American partner helped to get the internet connection to seismometers restored.  This, and the ensuing eruption, must have been worrying times for the Observatory.

2021 Eruption

Run Up to the 2021 Eruption

Reports on GVP for Mount Nyiragongo note that strong thermal anomalies and gas emissions were observed in the period June 2018 to May 2020, along with incandescence, seismicity and gas / steam plumes. 

In the period from June 2020 to November 2020, daily thermal activity was observed, indicating the presence of a large lava lake; levels of SO2 emissions fluctuated during the period. 

Eruption May 2021

Mount Nyiragongo erupted on 22 May 2021 at around 18:15 local time, sending torrents of low viscosity lava down the side of the volcano, reaching as far as the outskirts of Goma.  The following account of the eruption is summarised from bulletins on GVP.

The crater lava lake drained followed by the opening of at least two fissures on the south flank of the volcano. The first fissure’s lava originated near the Shaheru crater flowing eastwards over a main road; lava flows from the second fissure reached villages north of Goma destroying around 3,629 homes and buildings, displacing 20,000 to 25,000 people, and cutting off electricity and water supplies to parts of the city. Ash plumes, caused by collapse in the summit crater, rose initially to 45,000 feet then 20,000 to 30,000 feet. 

Eye witnesses report that no felt earthquake preceded this eruption, which is consistent with instrument monitoring.  Between 22 and 24 May 2021 earthquakes occurred between the summit and Lake Kivu.  Tremors were felt in Goma every 30 minutes from midday 23 May 2021. Cracks appeared in different parts of the city, stretching several hundred metres southwards to the lake, some emitting gases and flames. A 5.1 M earthquake occurred beneath Lake Kivu at 10:37 on 24 May 2021. Seismicity remained intense on 25 May with more than 130 earthquakes between 2M and 5M recorded in a 24-hour period. News reports indicated hundreds of damaged buildings in neighbouring Rwanda.  Rwanda suffered 13 earthquakes in excess of 4.0 between 23 May to 27 May 2021.  Seismicity has since decreased, although there is some evidence suggesting magma movement beneath the city of Goma.

The volcano is monitored by the Observatoire Volcanologique de Goma (OVG).  OVG have given four possible scenarios as to how the eruption could progress:

  1. A new fissure eruption on the southern flanks of the volcano;
  2. A new eruption with fissures in or extending to the cities.
  3. A new eruption with fissures extending to Lake Kivu.
  4. Activity subsides.

Lake Kivu contains dissolved gases, including CO2.  Heat or other disturbance from fissure activity beneath the lake may release dissolved CO2 in a cloud that could kill at lower elevations in its path.  Although the 2002 eruption did not cause a large gas release from the lake, you can never say never.

Background

Tectonic Setting

Nyiragongo is 3,470 m high stratovolcano with a 1.2 km wide summit crater which contained a small active cone and lava lake, located in the Virunga Mountains in the Kivu Rift on the western arm of the East African Rift.  The volcano’s edifice is built of lava flows and pyroclastics. Goma, with a population of 670,000 is located on the shores of Lake Kivu 12 km south of the volcano. 

Fig 2: Tectonic setting by the author: East African Rift System on the left; and, a close up of part of the Kivu Rift on the right.  Earthquakes and volcanoes delineate the rift system. Raw earthquake data for the period 1975 to 7 June 2021 obtained from USGS (see link below). Green dots denote earthquakes < 5.0M, light green dots, earthquakes between 5M and 6M, orange dots, earthquake between 6M and 7M, red stars, earthquakes >7M, blue filled triangles, Holocene volcanoes with known eruption dates, blue unfilled triangles, Holocene volcanoes whose dates of eruption are not known, orange filled triangle, Mount Nyiragongo. © Copyright remains with the author; all rights reserved, 2021.

Volcanic and tectonic activity in the area is complex, influenced by to the opening of the East African Rift System in the midst of pre-existing areas of crustal weakness.  The East African Rift System is a 3,000 km long continental rift extending from the Afar Triple Junction to western Mozambique.  The Nubian Plate is moving away from the Arabian and Somalia Plates.  Mantle plumes are thought to be the cause of doming and rifting. Rifting occurs at rates of 1 to 4mm a year, increasing north to south on the western arm of the rift and increasing south to north on the eastern arm.  The slower rate of rifting in the continental lithosphere results in different volcanism than oceanic crust settings.

The Kivu Rift was created c. 5 Ma; it extends between Lake Tanganyika to Lake Albert in the central part of the western branch of the East African Rift System in an area of uplift called the Kivu Dome.  There are two areas of volcanism associated with the rift, the South Kivu Volcanic Province and the Virunga Volcanic Province. Lake Kivu, itself, is a complex series of basins, the result of a rift depression whose waters drained northward until blocked by volcanic activity in the Virunga Volcanic Province c. 11,000 years ago, after which they flowed southwards.  We will focus on the Virunga volcanism.

The Virunga Mountains comprise eight volcanoes on the border between the Democratic Republic of the Congo, Rwanda and Uganda.  The volcanoes are: Mount Karisimbi, a 4,507m a complex basanitic-to-trachytic volcano , last known eruption 8050 BC; Mount Mikeno, a dormant 4,437m volcano; Mount Muhabura, 4,127m basanitic-to-trachyandesitic stratovolcano; Mount Bisoke, a 3,711m trachyandesitic stratovolcano, last eruption1957 ; Mount Sabyinyo, an extinct 3,674m volcano and the oldest in the range; Mount Gahinga, an extinct 3,474m volcano; Mount Nyiragongo,  a 3,470m foidite stratovolcano, last eruption 2021 ; and Mount Nyamuragira, a 3,058m high-potassium basaltic shield volcano, last eruption 2021.

In the Virunga Volcanic Province, volcanic activity occurred in two stages:  1) pre-rift doming which produced alkali basalts in west Virunga c. 13 Ma to 9 Ma, after which volcanic activity ceased; and, 2) the opening of a trans extensional fault zone with ENE-WSW displacement c. 2.6 Ma.

Mount Nyiragongo’s Lavas

The Virunga Volcanic Province lavas are leucite basanite (e.g., Nyamuragira) from primitive mantle at depths of between 80km to 150km, or a more enriched leucite-melilite nephelinite (e.g., Nyiragongo) from mantle source at the same depth which has been enriched by contact with a carbonatite source.  The source for the carbonatite is thought to be either from contact between rising magma and carbonate containing fluids or melt addition before or during magma generation 500 ma to 800 ma.

Nyiragongo’s melilite leucite nephelinite lavas are classed as foidite with minor basalt / picro basalt.  It is the low silica foidites that make her lava’s so fluid, despite the volcano being a stratovolcano. These lavas can reach a speed of 60 – 100 km per hour and, unlike most lavas, cannot be outrun.    The edifice, itself, is built of lava flows interspersed with pyroclastics. 

Mount Nyiragongo’s Historic Eruptions

Recording of Nyiragongo’s eruptions started in 1884.  GVP records 20 Holocene eruptions, all of which are VEI 1, except for the VEI 2 January 2002 eruption.  The most recent eruptions were in 1977, 1994, 2002 and now 2021. 

In 1991, Mount Nyiragongo was designated a Decade Volcano, worthy of study.

1977 Eruption

On January 10, 1977, a system of N-S fissures opened near the Baruta and Shaheru craters and the lava lake drained. Initial lava flows reached speeds of 100 km per hour due to the altitude of the fissures between 1,500m and 2,000m, combined with the low viscosity of the lava. The lava flow reached 20 km from the fissures.  600 people were killed.  A herd of elephants unfortunate enough to be caught up in the flow were preserved as lava formed moulds.

2002 Eruptions

Run Up to the 2002 Eruption

The 2002 eruption was preceded by seismic and fumarolic activity enabling warning to be given and the 400,000 residents in the hazard zone to be evacuated.  Initial long period events and volcanic tremors were recorded between December 2000 and January 2002.  Mount Nyamuragira erupted in February 2001 for two weeks but the seismicity remained high.  In October 2001, seismic activity increased and a tectonic earthquake between 3.5M and 4M was felt, followed by a high amplitude volcanic tremor.  White plumes were observed in the Shaheru and central craters and a dark plume was visible from the spatter cone accompanied by new fumarolic activity.    In January 2002, seismic activity increased again, along with a >4M earthquake and the resumption of fumarolic activity; an eight-hour lull in seismic activity preceded the onset of the eruption. 

Eruption January 2002

On 17 January 2002, a 13 km fissure system opened on the south side of the volcano which reached Lake Kivu; lava reached Goma, itself, covering part of the local airport’s runway and reaching the lake. Again, the initial speed of the lava was high at altitude but much lower in the vents nearer to Goma (0.1 to 1km per hour). Lava erupted from the higher parts of the fissure is thought to have temperatures of c.1370°C with little or no crystal content, whereas that closer to Goma was thought to have cooled to 1,320°C causing some crystallisation and increasing its viscosity.  Lava covered 4.7 km2, leaving 120,000 people homeless. 245 fatalities were caused by CO2 and buildings collapsing from lava and seismic activity.  A three-month seismic swarm which followed caused more building damaged.

Six months after the first eruption the volcano erupted again in 2002.

Current Status

For more information on the status of the current eruption, please refer to The Goma Volcano Observatory Face Book page: Observatoire Volcanologique de Goma OVG | Facebook or their partner’s site: GeoRiskA  Eruption of the Nyiragongo volcano | Georiska (africamuseum.be)

Let’s hope the volcano settles down or that future activity causes no harm.

The Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2021

Sources and Further Reading

Global Volcanism Program, Smithsonian Institution: https://volcano.si.edu

Raw earthquake data and “Seismotectonics of the East African Rift System”, USGS: https://earthquake.usgs.gov/earthquakes/

A. Pouclet, H. Bellon, K. Bram, “The Cenozoic volcanism in the Kivu rift: Assessment of the tectonic setting, geochemistry, and geochronology of the volcanic activity in the South-Kivu and Virunga regions”, Journal of African Earth Sciences, 121, (2016), 219-246: https://www.sciencedirect.com/

R. Gill, “Igneous Rocks and Processes A Practical Guide”, Wiley-Blackwell, 2010

P. Francis, C. Oppenheimer, “Volcanoes”, Second Edition, Oxford University Press, 2004

R. V. Fisher, G. Heiken, J. B. Hulen, “Volcanoes Crucibles of Change”, Princeton University Press, 1997

Famous Eruptions, Indonesia

Tambora 1815

This is the first of out famous eruptions series.  Why not start with one of the largest?

Fig 1: Tambora’s caldera by Tisquesusa, 2017; published under CC BY 4.0

Tambora produced one of the largest known eruptions in recorded history with a climate impacting VEI 7 and possibly the largest Holocene eruption (other contenders for a VEI 7 being Kurile Lake, 6440 BC, Mazama, 5700 BC, Kikai Caldera, 4300 BC, Cerro Blanco, 2300 BC, Thera (Santorini), 1620 BC, Taupo, 180 AD, Baekdu, 946 AD, and Samalas (Rinjani), 1257 ).

 Tambora’s once proud 4,300 m stratovolcano lost around a third of its height and acquired a 1 km deep, 6 km wide caldera over the space of a few days in April 1815.  Sumbawa and the surrounding islands were devastated. Climate abnormalities (cooling and severe storms) were noted round the northern hemisphere along with crop failure and famine.  Tambora is accredited as the cause of the 1816 “year without a summer”. The eruption released 50 km3 of magma, 150 km3 of tephra, 80 million tonnes of sulphur dioxide and 18 mega tonnes of fluorine, along with water vapour and other aerosols.

The eruption was chronicled by local eye witnesses.  However, the then lieutenant governor of Java, Sir Stamford Raffles, keen to develop trade in the area, was not so keen to broadcast it further afield to potential investors; outside the region, the eruption went largely unnoticed by the West, already distracted by the Napoleonic wars.

Geological Setting

Before the eruption, Sumbawa Island was a pleasant prosperous island, trading mung beans, corn, rice, coffee, pepper, cotton, wood and horses.  Despite a wealth of natural resources, the people to farm them were in short supply so there was also a large slave trade and piracy.

Tambora occupies the entire Sanggar Peninsula on Sumbawa Island in the Sunda Arc of the Indonesian Archipelago.  Here the Australian Plate subducts beneath the Sunda Plate at a convergence rate of 7.8 cm per year.  Plotting the earthquakes in the region for 1972 to date clearly shows the Wadati-Benioff zone, with volcanoes sitting around 70km above the descending plate. 

Fig 2: Scatter plot of the earthquakes showing the subduction zone (Wadati-Benioff zone) where the Australian Plate meets the Sunda Plate by the author.  Green dots represent earthquakes < 5M, yellow circles, 5M to 6M, red stars, >6M, blue triangles, some volcanoes. © All rights reserved, 2020

Tambora is a 60 km wide stratovolcano with trachybasalt and trachyandesite lavas.  She formed a caldera c.43,000 years ago which was in-filled by Pleistocene lava flows.  During the Holocene her eruptions have been explosive: three eruptions in the Holocene occurred before the 1815 event, identified by radiocarbon dating, 740 AD, 3050 BC, and 3910 BC; three further smaller eruptions have been observed since the 1815 event, 1819 VEI 2, 1880 VEI 2 and 1967 VEI 0, which extruded lava domes and small lava flows on the caldera floor.

1815 eruption

Tambora had been dormant for over a thousand years; magma cooling and fractional crystallisation had been occurring along with the exsolving of high-pressure magma; over pressurisation was happening. Tambora awoke in 1812 with minor activity during the period 1812 to 1815 while magma ascended from the reservoir c.4 km below the edifice. 

The 1815 eruption proper started with a short Plinian eruption on 5 April 1815 of trachyandesite, lasting two hours, producing a 33 km eruption column; the explosions were heard as far away as Sumatra and were confused with gun fire. Following this, between 5 April and 10 April, there was a relatively low level of activity. 

On the evening of 10 April, a second short Plinian eruption occurred, lasting three hours, producing a 44 km eruption column.  Pumice rained down on local villages for 2 hours.  Volcanic winds destroyed trees and property.  The eruption column collapsed as the vent was eroded.  Pyroclastic density currents (PDCs) raged over the next three to four days, creating phoenix ash clouds, covering the area in ash and destroying villages, along with inhabitants.  During this phase the volcano, no longer supported by magma, subsided, creating the current caldera.

Tsunamis were generated when the PDCs reached the sea.  Sanggar was engulfed in a four-metre high tsunami at around 10 pm on 10 April; this tsunami reached Java a couple of hours later with a height of two metres. 

Explosions were heard during the night of 10 to 11 April up to 2,600 km away.  Locations within a 600km radius suffered darkness for a couple of days and a chilling of the atmosphere while sunlight was blocked. 

Seven or more ignimbrite layers were deposited during the second phase of the eruption.  Only 2.6 km3 of deposits remain on dry land; the heavier ejecta ended up in the sea and lighter aerosols were scattered round the globe.  Pumice rafts up to 5 km wide and trees trunks littered the Flores Sea, providing a hazard for shipping for several months.

Eruptive activity continued intermittently up to August 1819. 

Local and global impact of the eruption

Sumbawa was stripped of its vegetation. The death toll in Sumbawa and neighbouring Lombok was in the order of 60,000, 10,000 from the eruption itself with the remainder from disease and famine from polluted water and loss of crops and livestock.  Children were sold into slavery in order for them to survive or apparently killed to avoid a slow death from starvation or worse. 

The effects were also global.  The volcano had lobbed 50 km3 of matter plus gases into the stratosphere.  Larger particles fell back to Earth but smaller aerosols hung around for three years causing adverse weather phenomena (e.g. storms), global cooling, failed harvests, famine and disease in much of the northern hemisphere.

The global effects were exacerbated, according to ice-core sampling, by another large catastrophic eruption in 1809.  The source for the 1809 has yet to be identified; the volcano and eye witnesses may not have survived the eruption.  However, the 1809 and 1815 eruptions together caused a little ice age.

Can this happen again?

VEI 7 eruptions are rare.  As mentioned earlier, there are currently only eight other contenders in the Holocene. That is not to say they won’t happen again in the future. 

My guess is that to get another large event, not only do you need a large magma source and a build-up of pressure but also an element of edifice failure.  The largest part of the Tambora eruption in terms of magma output was while the PDCs were in full swing; these occurred as or after the vent eroded.  We will see in the accounts of other eruptions, there was some edifice failure.

In the meantime, Mount Tambora and her Indonesian sisters are well-monitored.

The Armchair Volcanologist

6 July 2020 (updated 23/08/2020 & 25/08/2020 to include more potential VEI 7s (the list is getting longer!)

© Copyright remains with the author; all rights reserved, 2020

Sources and Further Reading

“Volcanoes, Earthquakes and Tsunamis”, David A. Rothery, Teach Yourself, 2010.

“Volcanoes”, Second Edition, Peter Francis, Clive Oppenheimer, Oxford University Press, 2004

“Tambora: The Eruption That Changed the World”, Gillen D’Arcy Wood, Princeton University Press, 2014

Mount Tambora – Wikipedia, https://en.wikipedia.org/wiki/Mount_Tambora

Earthquake data from Incorporated Research Institutions for Seismology (IRIS) Earthquake Browser: http://ds.iris.edu/ieb

Plot by the author.