Chronology of the eruption
Mount Tambora experienced several centuries of inactive
dormancy before 1815, as the result of the gradual cooling of
hydrous magma in a closed
magma chamber.
Inside the chamber at depths between 1,5 – 4,5 km, the
exsolution of a high-pressure fluid magma formed during cooling and
crystallisation of the magma. Overpressure of the chamber of about 4.000 – 5.000
bar was generated, and the temperature ranged from 700–850 °C.
In 1812, the
caldera began to rumble and generated a dark cloud.
On 5 April 1815, a moderate-sized eruption occurred, followed by
thunderous detonation sounds, heard in
Makassar on
Sulawesi, 380 km away, Batavia (now
Jakarta) on
Java 1,260 km away, and
Ternate on the
Molucca Islands 1,400 km away. On the morning of April 6,
volcanic ash began to fall in
East Java with faint
detonation sounds lasting until 10 April. What was first thought to be sound of firing guns was heard on April 10 on
Sumatra island (more than 2,600 km away).
At about 7 p.m. on 10 April, the eruptions intensified.
Three columns of flame rose up and merged.
The whole mountain was turned into a flowing mass of "liquid fire".
Pumice stones of up to 20 cm in diameter started to rain down at approximately 8 p.m., followed by ash at around 9–10 p.m. Hot
pyroclastic flows cascaded down the mountain to the sea on all sides of the peninsula, wiping out the village of Tambora. Loud explosions were heard until the next evening, 11 April. The ash veil had spread as far as
West Java and
South Sulawesi. A "nitrous" odour was noticeable in
Batavia and heavy
tephra-tinged rain fell, finally receding between 11 and 17 April.
The explosion is estimated to have been
VEI 7.
It had roughly four times the energy of the 1883
Krakatoa eruption, meaning that it was equivalent to an 800 megaton explosion. An estimated 160 km
3 of pyroclastic
trachyandesite was ejected, weighing approximately 1,4
14 kg. This has left a caldera measuring 6 – 7 km across and 600 – 700 m deep.
The density of fallen ash in
Makassar was 636 kg/m².
Before the explosion, Mount Tambora was approximately 4,300 m high,
one of the tallest peaks in the Indonesian archipelago. After the explosion, it now measures only 2,851 m.
The 1815 Tambora eruption is the largest observed eruption in recorded history.
The explosion was heard 2,600 km away, and ash fell at least 1,300 km away.
Pitch darkness was observed as far away as 600 km from the mountain summit for up to two days. Pyroclastic flows spread at least 20 km from the summit. Due to the eruption, Indonesia's Islands were attacked by tsunami waves reaching a height of up to 4 m.
Aftermath
All vegetation on the island was destroyed. Uprooted trees, mixed with pumice ash, washed into the sea and formed rafts of up to 5 km across.
One pumice raft was found in the
Indian Ocean, near
Calcutta on 1 and 3 October 1815.
Clouds of thick ash still covered the summit on 23 April. Explosions ceased on 15 July, although smoke emissions were still observed as late as 23 August. Flames and rumbling aftershocks were reported in August 1819, four years after the event.
A moderate-sized
tsunami struck the shores of various islands in the Indonesian archipelago on 10 April, with a height of up to 4 metres in Sanggar at around 10 p.m.
A tsunami of 1 – 2 m in height was reported in Besuki,
East Java, before midnight, and one of 2 metres in height in the
Molucca Islands. The total death-toll has been estimated at around 4,600.
The eruption column reached the
stratosphere, an altitude of more than 43 km.
The coarser ash particles fell 1 to 2 weeks after the eruptions, but the finer ash particles stayed in the
atmosphere from a few months up to a few years at an altitude of 10 – 30 km.
Longitudinal winds spread these fine particles around the globe, creating optical phenomena. Prolonged and brilliantly colored sunsets and twilights were frequently seen in
London, England between 28 June and 2 July 1815 and 3 September and 7 October 1815.
The glow of the twilight sky typically appeared orange or red near the horizon and purple or pink above.
The estimated number of deaths varies depending on the source. Zollinger (1855) puts the number of direct deaths at 10,000, probably caused by pyroclastic flows. On Sumbawa island, there were 38,000 deaths due to starvation, and another 10,000 deaths occurred due to disease and hunger on
Lombok island.
Petroeschevsky (1949) estimated about 48,000 and 44,000 people were killed on Sumbawa and Lombok, respectively.
Several authors use Petroeschevsky's figures, such as Stothers (1984), who cites 88,000 deaths in total.
However, Tanguy
et al. (1998) claimed Petroeschevsky's figures to be unfounded and based on untraceable references.
Tanguy revised the number solely based on two credible sources, q.e., Zollinger, who himself spent several months on Sumbawa after the eruption, and
Raffles's notes.
Tanguy pointed out that there may have been additional victims on
Bali and
East Java because of
famine and disease. Their estimate was 11,000 deaths from direct volcanic effects and 49,000 by post-eruption famine and epidemic diseases.
Oppenheimer (2003) stated a modified number of at least 71,000 deaths in total.