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The Eruption of Mount Tambora

Credible scientific evaluations can only be made on the basis of reliable data. Data collection is the time-proven starting point for all scientific inquiry. But the utility of data collection is not always evident at the time measurements and observations are entered in a record book; the payoff from a plodding exercise may be latent.  That is the case with Mr. Jefferson’s routine observations of weather at Monticello. On May 17, 1816, Jefferson wrote:

“…the spring has been unusually dry and cold. Our average morning cold for the month of May in other years has been 63º of Fahrenheit. In the present month it has been to this day an average of 53º, and one morning as low as 43º. Repeated frosts have killed the early fruits and the crops of tobacco of what will be poor.[1]

There is no evidence that, in 1816, Jefferson or any other American scientist made the connection between the most prodigious volcanic eruption in the history of civilization and drastic changes in weather in the United States—and elsewhere in the Northern Hemisphere. On April 10, 1815, the volcano Tambora in Indonesia had erupted violently (100,000 islanders killed) discharging the largest volume of sulfurous gases and volcanic ash from one natural source in recorded history. The blanket of fine particles that hung in the atmosphere reflected a substantial portion of solar radiation, causing what New Englanders referred to as the “Year of No Summer.”[2]

The fact that Jefferson did not connect the dots between cause and effect—he surely had heard of the Tambora disaster—does not diminish the importance of his data to science. Whenever scientists discuss the impact of Tambora, they tend to refer to Jefferson’s data; for, he used good weather instruments and he was consistent in observing and recording.[3]

In September 1816, Jefferson scanned his rainfall records and considered weather reports from elsewhere as he continued to puzzle over the drastic change in weather. This from his correspondence:

We have had the most extraordinary year of drought and cold ever known in the history of America. In June, instead of 3¾ inches, our average of rain for that month, we only had ⅓ of an inch; in August, instead of nine and one-sixth inches our average, we had only eight tenths of an inch; and it still continues. The summer, too, has been as cold as a moderate winter. In every State north of this there has been frost in every month of the year; in this state we had none in June and July, but those of August killed much corn over the mountains. The crop of corn through the Atlantic States will probably be less than one-third of an ordinary one, that of tobacco still less, and of mean quality.[4]

This is only one instance of the payoff to science from Mr. Jefferson’s passion for collecting basic data on natural phenomena.

- Edgar A. Imhoff, Monticello Research Report, May 2009


[1]  Jefferson to David Baillie Warden, 17 May 1816, in Betts, Garden Book, 557.

[2]  Monroe, James S. and Reed Wicander, The Changing Earth, 2nd ed. London: West/Wadworth, 1997.

[3]  Soon, Willie and Steven H. Yaskell, “Year Without A Summer,” Mercury 32, no. 3 (2003): 13-14.

[4]  Jefferson to Albert Gallatin, 8 September 1816, in Ford, 10:62-5.  Text available online.


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