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Vazquez R.,National Autonomous University of Mexico | Capra L.,National Autonomous University of Mexico | Caballero L.,National Autonomous University of Mexico | Arambula-Mendoza R.,University of Colima | Reyes-Davila G.,Centro Universitario Of Estudios vestigaciones En Vulcanologia
Journal of Volcanology and Geothermal Research | Year: 2014

Volcán de Colima is one of the most active volcanoes in Mexico where lahars are a common phenomenon. Since the reactivation of the volcanic activity in 1991, lahars have become more frequent during the June-October rainy season, in this region. Therefore, Volcán de Colima represents a natural laboratory, ideal for the constant monitoring of lahars and to study factors controlling their origin, flow transport and deposition. Since 2007 the systematic detection of lahars in Volcán de Colima has been carried out using seismic data from the broadband stations of the RESCO network, the seismological network of Colima University, along with three rain gauge stations located on the southern ravines of the volcano. In 2011 a new monitoring station was built at 2000. m.a.s.l. along the Montegrande ravine, which consists of a geophone, a video camera and a rain gauge station coupled with a moisture sensor, transmitting in real time to the RESCO facilities at Colima University. With all the instrumentation currently installed on the volcano flanks, we could monitor and describe the lahar that occurred on 15th September 2012 along the Montegrande ravine, and correlate the monitoring data with information gathered by the field campaign conducted two days after the event. The high quality of collected data enabled us to describe the "anatomy" of this lahar. The event consisted of a lahar that lasted 40min, triggered by 20mm of accumulated rainfall with a maximum intensity of 95mm/h. The lahar was characterized by three main surges at 4-5minute intervals that formed an 80cm-thick terrace. The first surge was a debris flow with a block-rich front followed by the main body that progressively diluted to a hyperconcentrated flow, from which a 40cm-thick massive unit was emplaced (33wt.% gravel and >60wt.% of sand); it was followed by a more dilute hyperconcentrated flow that left a massive 10cm-thick sandy layer (80wt.% of sand); the third surge deposited a 30-cm thick upper massive unit texturally similar to the first. Laminated layers separate the two first units. Subsequent surges were confined to the inner portion of the channel by the newly formed terrace. Based on flow depth estimation and difference in arrival times between geophones, a mean velocity of 3m/s and a maximum peak discharge of 48m3/s were estimated. Segregation processes that promote the upwelling of the largest clasts (20-30cm) on the flow surface were also observed, resulting in a clast-rich levee on top of the depositional units. A sedimentation rate of ~5-7cm/min was also determined. The results here obtained are useful to better understand textural features of lahar deposits from which important information on flow behavior can be interpreted. © 2013. Source

Vazquez R.,National Autonomous University of Mexico | Surinach E.,University of Barcelona | Capra L.,National Autonomous University of Mexico | Arambula-Mendoza R.,University of Colima | Reyes-Davila G.,Centro Universitario Of Estudios vestigaciones En Vulcanologia
Bulletin of Volcanology | Year: 2016

Volcán de Colima is one of the most active volcanoes in Mexico, not only for its eruptive history, but also for its annual occurrence of lahars. This makes the volcano a natural laboratory for monitoring and studying lahar processes. Since 2011, monitoring instruments have been deployed along the highly active Montegrande ravine, with at least three lahar events per year. Here, we report the datasets of three events collected during the 2012 and 2013 seasons, then interpret the acquired data. An event classification scheme based on lahar magnitude, duration and seismic characteristics is presented to distinguish “single-pulse” events (SPEs) from “multi-pulse” events (MPE). SPEs lasted approximately 60 min, had average velocities of ~2 m/s and mean peak discharges of ~24 m3/s. MPEs endured for more than 3 h, reached mean velocities of ~4.5 m/s and peak discharges of ~60 m3/s (for block-rich surges). The seismic signal-analysis also allowed us to discriminate physical flow fluctuations within single lahars, i.e. between the arrival of block-rich fronts and subsequent variations in flow discharge. The exponential regression analysis showed a best fit, with correlation coefficients around 0.92 and exponential coefficients of ~0.01 s, for the block-rich fronts, with seismic amplitudes increasing from 4.8 × 10−4 to 2.3 × 10−3 m/s and frequency ranges from 10 to 20 Hz. The variations in flow discharge were distinguished by lower amplitudes of ~5.7 × 10−4 m/s than those of the block-rich fronts and with frequency ranges of 10–40 Hz. The results presented in this paper demonstrate that the seismic data of events allowed us to describe and discriminate among different flow types; these records are thus a useful investigation tool for lahar events that have a seismic record but are not observed directly. We propose that a seismic early warning system can be developed to help civil protection authorities in designing risk mitigation strategies. © 2016, Springer-Verlag Berlin Heidelberg. Source

Arambula-Mendoza R.,National Autonomous University of Mexico | Lesage P.,CNRS Institute of Earth Sciences | Valdes-Gonzalez C.,National Autonomous University of Mexico | Varley N.R.,University of Colima | And 2 more authors.
Journal of Volcanology and Geothermal Research | Year: 2011

Volcán de Colima is considered the most active in Mexico. A period of large eruptive activity occurred in 2004-2005. It began as a swarm of long-period events (LPs) in late September 2004, indicating the onset of growth of a new lava dome in its crater. Subsequently, avalanches of incandescent material and pyroclastic flows during a period of approximately 2 months occurred. Then, the activity became more explosive with moderate explosions. Finally, swarms of LPs accompanied the magma ascent and extrusion of small domes and vulcanian explosions with pyroclastic flows in 2005. This eruptive period was investigated with a continuous seismic signal study, cross-correlation of LPs and autoregressive analysis of monochromatic LPs. For the vast majority of the explosions, an increase in the rate of seismic energy was observed with the Seismic Spectral Energy Measurement (SSEM) from 1 to 3. Hz, before each explosive event. This increase in energy is proportional to the increase in the rate of LPs, probably as a result of an increase in the emission rate. Applying the material failure forecasting method (FFM) and using SSEM inverse of parameter, the time of the explosions is estimated as the time when the adjusted line reaches the null value. We observe a systematic delay of a few hours between the real time of occurrence of the explosions and the estimated time. This suggests that more complex processes than pure damaging of the plug occur before the explosions. The swarms associated with the large explosions include a large proportion of LPs with similar waveforms. They form a dozen of families which stay during the whole period of activity and which indicate repetitive sources. Some of the families are active only before the explosions and could therefore be used as early warning. Monochromatic LP events occurred during this period, some of them just some hours before an explosion. However, no clear relationship between their occurrence and the explosions could be found. © 2011 Elsevier B.V. Source

Lesage P.,University of Savoy | Lesage P.,French National Center for Scientific Research | Reyes-Davila G.,Centro Universitario Of Estudios vestigaciones En Vulcanologia | Arambula-Mendoza R.,Centro Universitario Of Estudios vestigaciones En Vulcanologia
Journal of Geophysical Research: Solid Earth | Year: 2014

We used the ambient noise cross-correlation and stretching methods to calculate variations in seismic velocities in the region of Volcán de Colima, Mexico. More than 15years of continuous records were processed, producing long time series of velocity variations related to volcanic activity, meteorological effects, and earthquakes. Velocity variations associated with eruptive activity are tenuous, which probably reflects the open state of the volcano during the study period. Fifteen events among 26 regional tectonic earthquakes produced sharp, temporary decreases in seismic velocities, which then recovered progressively following a linear trend as a function of the logarithm of time. For the 15 events, the amplitude of the perturbation increased almost linearly with the logarithm of the amplitude of the seismic waves that shook the edifice. The most dramatic apparent velocity variation was a drop of up to 2.6% during the nearby M7.4 Tecomán earthquake in 2003. In order to locate the perturbation in the horizontal plane we applied an inverse method based on the radiative transfer approximation. We also used an original approach based on the frequency dependence of velocity variations to estimate the depth of the perturbation. Our results show that the velocity variation was well localized in the shallow layers (< 800m) of the volcano, with almost no variations occurring outside the edifice. We discuss several possible interpretations and conclude that the most plausible explanation for the velocity decreases is the nonlinear elastic behavior of the granular volcanic material and its mechanical softening induced by transient strains. ©2014. American Geophysical Union. All Rights Reserved. Source

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