Geomorphic processes and past climatic variations inferred from a tree-ring series, Trinchera Peak Area, Colorado.

Abstract

A set of 21 tree-ring cores was taken from 11 Colorado blue spruce (Picea pungens) and two Douglas fir (Pseudotsuga menziesii) in the vicinity of Trinchera Peak, Colorado. Annual and long-term variations in ring-width patterns show relationships to climatic variables. Cores taken from older trees near timberline were used as proxies for the local temperature record. Low summer temperatures control the growth of trees near timberline. Cores from near timberline document the effects of the Little Ice Age and the continuing warming of the Northern Hemisphere as the Earth recovers from the cold of the Little Ice Age. The effects of the Little Ice Age in this area became quite distinct about 1670. Warming began in the late 19th century. The eruption of Mount Tambora in mid-1815 depressed temperatures around the world. The year after the eruption (1816) was notably cold, and appears as a distinct event in several cores from near timberline. Cores taken from trees in the lower forest were used as proxies for local precipitation, and reveal a dry period between 1912 and 1930, and another dry period from 1950 through 1960. The second part of the study consisted of field observations of glacial erosion and deposition, and geomorphic processes present in the area. Climate controls geomorphic processes operating at this study area. Glaciers created much of the present landscape before the establishment of the forest. Quaternary deposits of the Trinchera Peak area include till, rock-glacier debris, and mass-movement deposits. Fluvial erosion, periglacial morphogenesis, and mass wasting are the dominant geomorphic processes operating today. Aerial photography was used to document the current landscape and the geomorphic processes that operate in the mountains.