Power spectrum crossover in sediments of a paleolake disturbed by volcanism G. Martínez-Mekler, E. Ugalde and G. Vilaclara Eur. Phys. J. Special Topics, 143 (2007) 217-222 Published online: 12 May 2007 DOI: 10.1140/epjst/e2007-00090-2