Reconstruction of gully erosion based on exposed tree roots in a recent landform of Paricutin Volcano, Mexico

Abstract

AbstractGullies in volcanic deposits are among the first signs of erosion that can be observed during or immediately after the volcanic activity and reflective of unstable conditions of newly formed deposits. Gully formation and erosion pulses may well continue to occur long after the initial landform was created, mostly as a result of torrential rainfall and/or land‐use changes. Yet, proper understanding of erosion dynamics and its relations with environmental drivers remains challenging as long‐term observations are, especially in volcanic terrain. Here we applied dendrogeomorphic approaches to (i) analyse both microscopic and macroscopic disturbances in tree roots exposed by gully erosion in a young volcanic landform of central Mexico and to (ii) quantify the evolution of erosion in the volcanic deposits of Paricutin Volcano. To this end we analysed 154 cross‐sections of 30 living, exposed roots of Pinus pseudoestrobus Lindl., of which 25 were used for anatomical and 129 for macroscopic analysis. Wood anatomical – or microscopic – disturbances were mostly in the form of strong growth reductions (~50%) in lumen area of earlywood tracheids, substantial increases in ring widths (mostly stemming from eccentric growth) and the increased formation of latewood cells. We observe major erosion pulses in 2010, 2012, 2015, 2016, 2017 and 2018, triggered primarily by torrential rainfall (with >100 mm 24 h−1 for the maximum intensity event: standard precipitation index values ≥ 2). Along the gully, the lower sector formed between 2009 and 2017, whereas the central sector exhibited important phases of exposure from 2012 to 2018. In the upper, most recent sector of the gully, erosion started only in 2017. Erosion rates in the lower and upper sectors are smaller with a channel widening rate of 6 to 16 cm yr−1. Around the main knickpoint found in the central part of the gully, retreat rates are up to 60 cm yr−1 and gully incision is 30 cm yr−1. The methods applied in this research are novel and can be applied to other volcanic environments with intense gully erosion, so as to provide baseline data for land‐use and environmental management plans.