Mount Tambora eruption (1815) investigation

01 · The briefing

Begin with the question.

In April 1815, Mount Tambora on Sumbawa island, in present-day Indonesia, erupted in what NASA describes as the largest eruption in recorded history. Ash and gases reached the upper atmosphere, and the following year became known as a 'year without a summer'. In New England it was remembered for six inches of June snow, frost in every month and lost crops. The connection is attractive: one geophysical event seems to explain a widespread disruption.

Three explanations compete in popular accounts. The first treats Tambora as the sole cause of the cold. The second attributes the cold to ordinary natural variability, the normal swing of summer weather. The third treats the hardship as mainly a failure of farming, markets and trade. This investigation asks what physically links the eruption to the climate, what kinds of evidence support that link, and how far any single cold summer can be attributed to one volcano. The answer depends on separating a physical mechanism from particular weather events, and on distinguishing measured temperatures from crop failures, which had many contributors.

Wide photo of a caldera rim with a lake in the crater and cloud cover above. — Where it happenedLater photograph A panorama of the Tambora caldera, photographed long after the eruption. Photo: Tisquesusa · CC BY 4.0 · Wikimedia Commons.

The timeline

1812-1815
Tambora is active, according to NASA's account of the volcano's history before the main eruption.
1815-04-10
The major eruption; NASA estimates about 150 cubic kilometres of tephra, with ash recognised at least 1,300 kilometres away.
1816, June-August
The central England summer mean is about 13.4 degrees Celsius, third-coldest of the 368 summers from 1659 to 2026, by Faultory's ranking of the Met Office monthly means.
1816
New England records a 'year without a summer', with six inches of snow in June and hard frost in every month, according to the New England Historical Society.
2015-07-08
Sigl and colleagues publish in Nature a study of the timing and climate forcing of volcanic eruptions over the past 2,500 years.

A researched reconstruction for learning. These reasoning steps simplify a complex record; no score can capture the full history.

02 · The evidence

What does the record show?

Photo of a slope with layered dark and light volcanic deposits and sparse vegetation. — On the evidence tableLater photograph Layered tephra deposits near the summit of Mount Tambora, photographed long after the eruption. Photo: Tisquesusa · CC BY 4.0 · Wikimedia Commons.

Read each exhibit before settling on an explanation. The source links below every exhibit lead to the record behind it.

Exhibit 01

A plume that reached the upper atmosphere

NASA's Earth Observatory describes the 10 April 1815 eruption as producing an estimated 150 cubic kilometres of tephra, with ash recognised at least 1,300 kilometres away, and states that enough ash entered the atmosphere to reduce sunlight and cause global cooling, leading to the 1816 'year without a summer'. The account describes the mechanism in terms of ash. It does not measure 1816 temperatures.

Source record s1science.nasa.gov

Exhibit 02

Ice cores and tree rings

The Nature study by Sigl and colleagues resolves inconsistencies between the timing of volcanic aerosol loading recorded in ice cores and the cooling recorded by tree rings. The authors conclude that large tropical and high-latitude eruptions were primary drivers of Northern Hemisphere temperature variability over the past 2,500 years. Its extended data includes a subset of eruptions with sulfate loadings larger than Tambora 1815's.

Source record s2nature.com

Exhibit 03

A weather record for central England

The Met Office Central England Temperature series gives monthly means from 1659. The June-August mean for 1816 is about 13.4 degrees Celsius, against about 14.8 for 1815 and 14.3 for 1817. Ranking the published monthly means (Faultory's own calculation) places the 1816 summer third-coldest of the 368 summers from 1659 to 2026. This is a single region, and it shows a cold summer, not its cause.

Source record s3metoffice.gov.uk

Exhibit 04

Crop failures in New England

The New England Historical Society describes six inches of snow in June, hard frost in every month, and July and August temperatures as low as 40 degrees Fahrenheit as far south as Connecticut. It reports destroyed bean crops, hay shortages that forced livestock slaughter, hoarding and price rises. This is a secondary summary. It shows consequences of a cold year, which had several contributors.

Source record s4newenglandhistoricalsociety.com

Exhibit 05

Testing one eruption against many

The Nature study uses a superposed-epoch analysis across sets of large eruptions, including the 28 largest, the 23 largest tropical eruptions and those larger than Tambora, measuring tree-ring growth 15 years after sulfate deposition. This tests whether large eruptions are followed by cooling as a set. A single summer such as 1816 cannot be tested that way on its own.

Source record s2nature.com

03 · Your reasoning

Follow the strongest explanation.

Choose an interpretation, then compare it with the evidence. You can revise your choice. The goal is understanding, not a perfect score.

Reasoning step 01 of 03

Which evidence most directly links the 1815 eruption to cooling in 1816?A literary work written during a cold, wet summer near Lake Geneva.The connection is an anecdote about a cold summer, not a climate measurement, so it cannot link the eruption to temperature.A single cold month recorded in one town.One station shows local weather, not a physical cause. A link to the eruption needs a pattern across events.Ice-core sulfate timing compared with later tree-ring cooling across many large eruptions.The Nature study uses ice-core and tree-ring evidence to resolve timing and tests large eruptions as a set.

Evidence-based explanation

This is the chain of evidence that links deposition timing to a measured temperature response across events. It is statistical: it shows that large eruptions are associated with cooling, not that one eruption caused one particular summer.

Weigh it against

Exhibit 02Ice cores and tree rings Exhibit 05Testing one eruption against many

Reasoning step 02 of 03

Why do the sources emphasise material lofted into the stratosphere rather than the local ash fall near the volcano?Local ash fall on Sumbawa cooled the whole planet directly.Local deposits are damaging nearby, but the global cooling in these accounts is attributed to material lofted high into the atmosphere.Fine material lofted into the stratosphere can stay aloft long enough to reduce sunlight over large regions.NASA states that enough ash entered the atmosphere to reduce sunlight, and the ice-core records track sulfate, the aerosol usually tied to cooling.Ice cores cannot record volcanic material, so the link must come from weather records alone.Ice cores preserve volcanic sulfate, which is the basis of the timing evidence in the Nature study.

Evidence-based explanation

The stratospheric route is the mechanism the sources share. The caveat is that NASA emphasises ash while the Nature study tracks sulfate. The mechanism is therefore described at the level of aerosols rather than as a single measured chain.

Weigh it against

Exhibit 01A plume that reached the upper atmosphere Exhibit 02Ice cores and tree rings

Reasoning step 03 of 03

How should a crop failure in New England be weighed as evidence about the eruption?As consistent with volcanic cooling, but also needing the weather record and other causes such as markets and farm practice.The New England account describes hoarding and price rises, which mix weather with market behaviour, so a weather record alone does not settle the cause.As proof that Tambora alone caused every failed harvest in the region.This overreaches. One summary cannot isolate the eruption from weather variability or from the economic response.As irrelevant, because the weather records already tell the whole story.Temperature records show the climate, but harvests also depend on rainfall, timing, markets and practice, so the records do not settle the outcome.

Evidence-based explanation

A crop failure is a downstream effect shaped by weather, markets and farming practice. It can corroborate a cold year but cannot isolate the eruption as its cause.

Weigh it against

Exhibit 04Crop failures in New England Exhibit 03A weather record for central England

04 · The findings

The chain behind the outcome.

The sources support a chain of reasoning. A very large eruption in April 1815 injected material into the upper atmosphere, and the cold that followed in 1816 is attributed to that material reducing sunlight. NASA's account makes this link in terms of ash. The Nature study, which compares ice-core timing with tree-ring cooling, supports the broader claim that large eruptions drive Northern Hemisphere temperature variation, and its extended data uses Tambora 1815 as a reference size for a subset of large eruptions.

The weather record shows the 1816 summer as exceptionally cold in central England. The June-August mean of about 13.4 degrees Celsius is among the three lowest in a series that starts in 1659. The New England account describes frost in every month, snow in June and crop losses, with hoarding and price rises. These are consistent with a cold year, though they are not measurements of the eruption.

The reconstruction should separate three levels. The eruption and the stratospheric aerosol are physically well supported in outline. The association between large eruptions and cooling is supported statistically across events. The claim that Tambora caused a particular cold summer or particular crop failures is an attribution that one region and one year cannot prove, because weather varies and economies respond to shortages in their own ways.

Colour map of Europe shaded blue over the west and orange over the east, with a scale from minus 3.5 to plus 3.5. — How it endedReconstruction A reconstruction of summer 1816 temperature anomalies in Europe, relative to 1971–2000, based on NOAA paleoclimate data. Photo: Giorgiogp2 · CC BY-SA 3.0 · Wikimedia Commons.

Contributing causes and conditions

A very large eruption on 10 April 1815 injected ash and gases high into the atmosphere.
Material spread in the stratosphere reduced the sunlight reaching the surface.
The cooling persisted through the 1816 growing season, bringing frost and crop losses in several regions.
Local weather variability and food markets shaped how severe the outcomes were in each place.
The link to one eruption is strongest in the pattern across many events, not in any single summer.

OutcomeMount Tambora eruption (1815)

Take the method with you

A physical mechanism can be well supported while an attribution to one specific event remains uncertain.
Test an event against a set of comparable events rather than a single memorable case.
Separate a measured weather anomaly from its social consequences, which have many causes.

You can read findings at any time. Exploring every reasoning step marks this case as complete in your notebook.

Open another investigation

The open record

Sources & further reading

Read the original record and its scope before relying on a conclusion. Source references support the exhibit summaries; Faultory’s reasoning prompts are editorial reconstructions.

s1
NASA Earth Observatory - Mount Tambora Volcano, Sumbawa Island, Indonesia
science.nasa.gov
s2
Nature - Sigl et al., Timing and climate forcing of volcanic eruptions for the past 2,500 years (2015)
www.nature.com
s3
Met Office Hadley Centre - HadCET Central England Temperature data download
www.metoffice.gov.uk
s4
New England Historical Society - 1816: The Year Without a Summer
www.newenglandhistoricalsociety.com

Written and curated for Faultory by Yunus Emre Vurgun, with AI-assisted research and drafting. Sources and interpretations can need correction. Read our editorial standards or report an issue.

The cold summer after Tambora