Tambora and the 'year without summer'

Tambora is a massive stratovolcano and forms the entire 60-km-wide Sanggar Peninsula on northern Sumbawa Island. The volcano originally grew to about 4000 m elevation before a major explosion destroyed its summit and left a pre-1815 caldera more than 43,000 years ago. Lava flows had largely filled the early caldera by about 10,000 years ago, before its activity changed to dominantly explosive eruptions, culminating in the 1815 eruption.

In April 1815, now over two centuries ago, the Tambora volcano in Indonesia erupted, but North America and Europe did not notice its effects until months later. The next year, 1816, became widely known as 'the year without a summer', as gases, ashes and dust drifted over the entire globe, reaching the stratosphere, where they remained long enough to create 'an enormous sun filter'.

A scientific study looked at the impact of this atmospheric phenomenon on agricultural production in the Iberian Peninsula in 1816 and 1817[1].

The year 1816 was characterised by great anomalies, especially in the summer, which was much colder and wetter than usual. In Madrid, temperatures were below 15ºC in July and August, and that Autumn the Catalan peaks of Montserrat and Montseny were covered with snow and the Llobregat river froze over.

The study includes information from the first instrumental observations carried out on the Peninsula by scientists in Lisbon, Madrid, Barcelona and San Fernando de Cádiz. It also brings together Spanish and Portuguese documentary sources, such as private diaries (for example that of Baron Maldá of Barcelona), which provide qualitative information about the weather, and religious documents including weather-related prayers.

Baron Maldá wrote in his diary that the unusual temperatures in the summer of 1816 could have been related to a 'great snowfall' in the centre of Spain on July 16. He also pointed out that it 'was snowing considerably' in the Pyrenees and the north of Europe. According to the scientists, this information coincides with the low temperatures of 13.1º recorded that day in Madrid. The apparent snowfall mentioned by the Baron may in fact have been a hail storm.

The eruption of the Tambora volcano was probably 'the greatest recorded eruption in historical times,'according to the researchers. This is demonstrated by its explosivity index (a measurement of the size of the eruption), which, at 7, was greater than any other more recent eruption, including that of Mount Pinatubo in the Philippines in 1991.

The consequences of the eruption were noticed not only on the climate, but above all on agriculture. The low temperatures meant that many crops did not ripen, or if they did their yield was very little and very late.

The decade from 1811 to 1820 was marked by serious socioeconomic impacts resulting from this poor agricultural production, with malnutrition and the increase of epidemics in Europe and Mediterranean countries. Low temperatures, freezing temperatures in Spring and heavy precipitation between 1816 and 1817 affected the growth of many crops very badly.

The cold and wet summer led to fruits being of poor quality, as well as vines and cereals ripening very slowly, which impacted on harvests. The climatic anomalies were more consistent in Lisbon and Cadiz, showing that the phenomenon in the Iberian Peninsula was not the same as in central Europe.

At the moment the Tambora volcano is considered 'restless'. Since 2013, the alert level is listed as 2 on a scale of 1-4.

[1] Trigo et al: Iberia in 1816, the year without a summer in International Journal of Climatology - 2009