Spatiotemporal Trends of Volcanism in the Altiplano Puna Volcanic Complex, Central Andes, South America

Introduction
GIS is an excellent tool to measure spatiotemporal trends of volcanism. This project examines the remote highlands of the central Andes in order to trace the patterns of volcanism on the highest volcanic plateau on earth. The Altiplano Puna Volcanic complex (APVC) is also home to some of the largest, most explosive eruptions ever recorded. Numerous catastrophic eruptions over the past 10 million years have blanketed the landscape with large sheets of ignimbrite. Although volumetrically minor, the effusive volcanic products also tell an important part of the APVC. This project examines the spatial distribution of effusive and volcanic products and examines the changing patterns of volcanism over the time span of the APVC.

Conceptual Model
The conceptual model for this project is shown below. The red outline highlights the part of the project that involves field work and laboratory analysis that I will do as part of my dissertation. The model presented here utilizes available data

Data Sources
The base layers for the project are an SRTM digital elevation model (DEM) and Landsat 3 band false colored satelite imagery. These are shown below. The extent of each digital data set is 21-24 degrees S and 66-69 degrees W. The SRTM DEM was projected to the UTM coordinates of the Landsat data. The SRTM data were downloaded from the USGS and the Landsat data were downloaded from NASA .

The spatial data for this study were created from geologic maps of the Bolivian section of the Altiplano Puna Volcanic Complex (APVC). The geologic maps were stitched together from individually scanned paper maps. These maps were then overlain on the SRTM and Landsat digital models.

Data Analysis
The geologic units on the map were traced in ArcMap to create polygons for both the effusive and the explosive eruptive products. In the APVC, nearly everything on the surface looks like it just came out of a volcano. Radiometric ages provided by the geologic maps were assigned as attributes to the polygons. Only 39 of the 149 traced effusive units and 24 of the 50 explosive units contain radiometric data. The units with ages are shown in color below. Units without ages are shown as outlines. Ages are in millions of years

Results The mean center of volcanism for the effusive (circles) and explosive (squares) polygons were calculated at 2.5 million year intervals using the GIS analytical functions. Because viscous effusive lava does not flow far from its vent, the effusive polygons are assumed to better represent vent locations than the explosive products which can travel far from the vent. However, both data sets are in good agreement suggesting that the explosive and effusive volcanism is correlated in time and space in the APVC. In addition, there is an apparent westward trend of volcansim as the volcanic center ages. More comprehensive coverage and better constrained data are necessary to test these conclusions.