Use of remote imagery to analyse changes in morphology and longitudinal large wood distribution in the blanco river after the 2008 chaitén volcanic eruption, southern chile

Abstract

The 2008 haitén volcanic eruption generated significant changes in the channel morphology and large wood () abundance along the fluvial corridor of the lanco iver, southern hile. Comparisons of remote sensing images from the pre‐eruption (year 2005) and post‐eruption (years 2009 and 2012) conditions showed that in a 10.2 km long study segment the lanco iver widened 3.5 times from 2005 to 2009, and that the maximum enlargement was nine times the original width. Changes in channel width were lower between the years 2012 and 2009. The sinuosity and braiding indexes also changed between 2005 and 2009. After the eruption the channel sinuosity was higher and specific river reaches developed a braided pattern, but by 2012 the channel was recovering pre‐eruption characteristics. Huge quantities of were introduced to the study segment; individual per km of channel length were 1.6 and 74.3 in 2005 and 2009, respectively, and more than 30 log jams km⁻¹ were observed in the year 2009. Between 2009 and 2012 the quantity of was very similar. Statistically significant relationships were found between the number of log jams and channel sinuosity and between the number of pieces of large wood with sinuosity and channel width. Wood was highly dynamic between 2009 and 2012: 78% of individual pieces and 48% of log jams identified in the 2009 image had moved by 2012. Finally the supervised classification of imagery associated with ArcMap tools was tested to identify large wood.

Key words:

• Chaitén volcanic eruption
• channel morphologic changes
• large wood distribution
• supervised classification
• Blanco River

Acknowledgements

This study is part of a doctoral thesis in Forest Sciences, Universidad Austral de Chile, and is supported by Project FONDECYT 1110609. Héctor Ulloa received a grant from the Chilean Comisión Nacional de Investigación Científica y Tecnológica (CONICYT).

Additional information

Notes on contributors

Héctor Ulloa

Héctor Ulloa, Universidad Austral de Chile, Graduate School, Faculty of Forest Sciences and Natural Resources, Isla Teja s/n, Valdivia, Chile

Andrés Iroumé

Andrés Iroumé, Silvia Diez, Universidad Austral de Chile, Faculty of Forest Sciences and Natural Resources, Isla Teja s/n, Valdivia, Chile

Luca Mao

Luca Mao, Pontificia Universidad Católica de Chile, Department of Ecosystems and Environment, Casilla 306 Correo 22, Vicuña Mackenna 4860, Comuna Macul, Santiago, Chile

Andrea Andreoli

Andrea Andreoli, Universidad de Concepción, Department of Forestry and Environmental Management, Concepción, Chile and Free University of Bozen‐Bolzano, Faculty of Science and Technology, Piazza Università 5, K Building, 39100, Bozen‐Bolzano, Italia

Luis E. Lara

Luis E. Lara, Servicio Nacional de Geología y Minería, Volcano Hazards Program, Avda. Santa María 0104, Santiago, Chile