Tree Rings and Ancient Climatic Conditions

Activity Source: 

Adapted with permission by Archaeological Institute of America.

How do archaeologists learn about climatic conditions and their effects on people in the past? In 1815, Mount Tambora in Indonesia erupted so violently that the sound of the eruption could be heard 1,600 miles away. Gases from the volcano shot into the stratosphere almost six miles above the Earth’s surface and lingered for years. Sulfur dioxide combined with water molecules to form sulfate particles that reflected sunlight away from Earth, gradually causing the planet’s surface to cool. The colder temperatures caused severe weather events worldwide.

Archaeologists know about some negative effects of the eruption from historical documents that record crop failures, cold temperatures, and scarce food and fuel. The eruption and its effects also affected tree growth- a clue to the past for archaeologists.

In the cross section of a tree trunk, you will see a series of rings. Every year a tree is alive, it grows a little wider, and that growth is represented by a ring. A ring has two parts. The wider, lighter-colored portion represents the beginning of the growing season. The darker, thinner part represents the latter part of the season. The width of a ring depends on the weather. In years with sufficient rain and warmth, rings are wider; but dry or cold years produce thinner rings.


  1. See the sample cross sections of trees provided here. The cross sections are arranged with the oldest, innermost ring for each tree to the left and the most recent, outermost ring to the right. The ring for the year 1819 is marked across all cross sections. For each sample, do the following steps.
  2. Determine the year in which the sample was taken and the number of years represented in each sample.
  3. Using the date line provided, find the tree rings for 1815 (the year of eruption). What do the rings on either side of the eruption look like? How was growth affected?
  4. How is cross section D different from the rest? How do you explain that?
  5. If you were an archaeologist, what other than tree rings could you look at for evidence of the effect of Tambora’s eruption on people?