A shield volcano is a type of volcano that has been formed by lava flow. Shield volcanoes are large and wide with a low profile. The crater at the volcano is not far above sea level in comparison to a composite volcano. Most shield volcanoes are super-volcanoes.

A shield volcano is a volcano with shallow-sloping sides. Shield volcanoes are formed from fluid lava that can travel long distances across slight inclines, resulting in their relatively flat, broad profile. In contrast, steeply sloped stratovolcanoes better match the popular stereotype of a volcano.

Some of the largest volcanoes on Earth are shield volcanoes

Q: What are some interesting facts on Mount Tambora

A: Use of the radiocarbon dating technique has established the dates of three of Mount Tambora's eruptions prior to the 1815 eruption. The magnitudes of these eruptions are unknown.[20] The estimated dates are 3910 BCE ± 200 years, 3050 BCE and 740 CE ± 150 years. They were all explosive central vent eruptions with similar characteristics, except the lattermost eruption had no pyroclastic flows. In 1812, Mount Tambora entered a period of high activity, with its climactic eruption being the catastrophic explosive event of April 1815.

Follow-up activity was recorded in August 1819 consisting of a small eruption (VEI = 2) with flames and rumbling aftershocks, and was considered to be part of the 1815 eruption sequence.[7] Around 1880 ± 30 years, Tambora went into eruption again, but only inside the caldera. Small lava flows and lava dome extrusions were formed. This eruption (VEI = 2) created the Doro Api Toi parasitic cone inside the caldera.[21]

Mount Tambora is still active. Minor lava domes and flows have been extruded on the caldera floor during the 19th and 20th centuries.[1] The last eruption was recorded in 1967.[20] However, it was a very small, non-explosive eruption.

1815 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 (0.93-2.8 mi), 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 (58,000-73,000 psi) was generated, and the temperature ranged from 700-850 °C (1292-1562 °F). 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 (240 mi) away, Batavia (now Jakarta) on Java 1,260 km (780 mi) away, and Ternate on the Molucca Islands 1,400 km (870 mi) away. On the morning of 6 April, 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 10 April on Sumatra island (more than 2,600 km or 1,600 mi 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".[22] Pumice stones of up to 20 cm (7.9 in) 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 first explosions were heard on this Island in the evening of 5 April, they were noticed in every quarter, and continued at intervals until the following day. The noise was, in the first instance, almost universally attributed to distant cannon; so much so, that a detachment of troops were marched from Djocjocarta, in the expectation that a neighbouring post was attacked, and along the coast boats were in two instances dispatched in quest of a supposed ship in distress.

-Sir Stamford Raffles' memoir.[22]

The explosion is estimated to have been VEI 7.[23] It had roughly four times the energy of the 1883 Krakatoa eruption, meaning that it was equivalent to an 800 Mt (3.3×1012 MJ) explosion. An estimated 160 km3 (38 cu mi) of pyroclastic trachyandesite was ejected, weighing approximately 1.4e14 kg (3.1×1014 lb) .This has left a caldera measuring 6-7 km (3.7-4.3 mi) across and 600-700 m (2,000-2,300 ft) deep.[5] The density of fallen ash in Makassar was 636 kg/m² (130.3 lb/sq ft).[24] Before the explosion, Mount Tambora was approximately 4,300 m (14,100 ft) high,[5]one of the tallest peaks in the Indonesian archipelago. After the explosion, it now measures only 2,851 m (9,354 ft).[25]

The 1815 Tambora eruption is the largest observed eruption in recorded history (see Table I, for comparison).[5][7] The explosion was heard 2,600 km (1,600 mi) away, and ash fell at least 1,300 km (810 mi) away.[5] Pitch darkness was observed as far away as 600 km (370 mi) from the mountain summit for up to two days. Pyroclastic flows spread at least 20 km (12 mi) from the summit. Due to the eruption, Indonesia's Islands were attacked by tsunami waves reaching a height of up to 4 m (13 ft).

Aftermath

On my trip towards the western part of the island, I passed through nearly the whole of Dompo and a considerable part of Bima. The extreme misery to which the inhabitants have been reduced is shocking to behold. There were still on the road side the remains of several corpses, and the marks of where many others had been interred: the villages almost entirely deserted and the houses fallen down, the surviving inhabitants having dispersed in search of food.

...

Since the eruption, a violent diarrhoea has prevailed in Bima, Dompo, and Sang'ir, which has carried off a great number of people. It is supposed by the natives to have been caused by drinking water which has been impregnated with ashes; and horses have also died, in great numbers, from a similar complaint.

-Lt. Philips, ordered by Sir Stamford Raffles to go to Sumbawa.[22]

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 (3.1 mi) across.[5] One pumice raft was found in the Indian Ocean, near Calcutta on 1 and 3 October 1815.[7] 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 (13 ft) in Sanggar at around 10 p.m.[5] A tsunami of 1-2 m (3.3-6.6 ft) in height was reported in Besuki, East Java, before midnight, and one of 2 metres (6.6 ft) 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 (27 mi).[7] 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 (6.2-19 mi).[5] 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.[5] 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.[27]Petroeschevsky (1949) estimated about 48,000 and 44,000 people were killed on Sumbawa and Lombok, respectively.[28] Several authors use Petroeschevsky's figures, such as Stothers (1984), who cites 88,000 deaths in total.[5] However, Tanguy et al.. (1998) claimed Petroeschevsky's figures to be unfounded and based on untraceable references.[8] 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.[22] 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.[8] Oppenheimer (2003) stated a modified number of at least 71,000 deaths in total, as seen in Table I below.[7]

Global Effects

Sulfate concentration in ice core from Central Greenland, dated by counting oxygen isotope seasonal variations. There is an unknown eruption around 1810s. Source: Dai (1991).[30]

The 1815 eruption released sulfur into the stratosphere, causing a global climate anomaly. Different methods have estimated the ejected sulfur mass during the eruption: the petrological method; an optical depth measurement based on anatomical observations; and the polar ice core sulfate concentration method, using cores from Greenland and Antarctica. The figures vary depending on the method, ranging from 10 to 120 million tons.[7]

In the spring and summer of 1815, a persistent dry fog was observed in the northeastern United States. The fog reddened and dimmed the sunlight, such that sunspots were visible to the naked eye. Neither wind nor rainfall dispersed the "fog". It was identified as a stratospheric sulfate aerosol veil.[7] In summer 1816, countries in the Northern Hemisphere suffered extreme weather conditions, dubbed the Year Without a Summer. Average global temperatures decreased about 0.4-0.7 °C (0.7-1.3 °F),[5] enough to cause significant agricultural problems around the globe. On 4 June 1816, frosts were reported in Connecticut, and by the following day, most of New England was gripped by the cold front. On 6 June 1816, snow fell in Albany, New York, and Dennysville, Maine.[7] Such conditions occurred for at least three months and ruined most agricultural crops in North America. Canada experienced extreme cold during that summer. Snow 30 cm (12 in) deep accumulated near Quebec City from 6 to 10 June 1816.

1816 was the second coldest year in the northern hemisphere since 1400 CE, after 1601 following the 1600 Huaynaputina eruption in Peru.[23] The 1810s are the coldest decade on record, a result of Tambora's 1815 eruption and other suspected eruptions somewhere between 1809 and 1810 The surface temperature anomalies during the summer of 1816, 1817 and 1818 were −0.51 °C (−0.92 °F), −0.44 °C (−0.79 °F) and −0.29 °C (−0.52 °F), respectively.[23] As well as a cooler summer, parts of Europe experienced a stormier winter.

This pattern of climate anomaly has been blamed for the severity of typhus epidemic in southeast Europe and the eastern Mediterranean between 1816 and 1819.[7] The climate changes disrupted Indian monsoons causing three failed harvests and famine contributing to worldwide spread of a new strain of cholera originating in Bengal in 1816.[31] Much livestock died in New England during the winter of 1816-1817. Cool temperatures and heavy rains resulted in failed harvests in the United Kingdom of Great Britain and Ireland. Families in Wales traveled long distances as refugees, begging for food. Famine was prevalent in north and southwest Ireland, following the failure of wheat, oat and potato harvests. The crisis was severe in Germany, where food prices rose sharply. Due to the unknown cause of the problems, demonstrations in front of grain markets and bakeries, followed by riots, arson and looting, took place in many European cities. It was the worst famine of the 19th century/ 1800s.[7]