Tree-rings based analysis of the 2001 pyroclastic flow and post-eruptive tree colonization on Popocatépetl volcano, Mexico

Abstract

Lava flow, pyroclastic flows and ash deposition can impair the vitality and growth of tree growing on or next to volcanoes, and sometimes even remove entire forest stands. In the case that trees are only injured, but not killed, past volcanic process activity can be analyzed through the growth disturbances left in the tree-ring records. We investigated disturbances in growth ring series of Pinus hartwegii trees associated with a pyroclastic flow that covered portions of the northern flank of Popocatépetl volcano on 22 January 2001. In addition, we also documented the post-eruptive colonization of trees on the resulting deposit. The pyroclastic flow burned and killed at least 190 trees and locally shifted the timberline downslope by ~40 m in elevation. A large number of trees were injured to show noticeable fire scars. We analyzed and characterize the damage in flow-surviving trees. Sixteen years after the event, whorl counts on 244 P. hartwegii shoots growing on the surface of the pyroclastic flow deposit showed average ages of 8 yr (this is the age at ~1.4 m height). The ecesis interval or Germination Lag Time (GLT) of trees on the pyroclastic flow deposit was 7 yrs (±2 yr), and the Colonization Time Gap (CTG) was 15 yrs on average (CTG is the sum of GLT and the interval between seedling germination and growth at ~1.4 m height), with local differences related to altitude and/or location on the bare surface. Results obtained at this site can be used to date and to identify the extent of pyroclastic flow deposits on active volcanoes, thereby providing valuable information on the volcanic history (in terms of frequency and runout distances) and therefore also for hazard prevention plans. In addition, it can be useful to calibrate the minimum ages of volcanic landforms.