Ashfall characteristics and development of the ash monitoring network during three decades of the long-lived eruption of Popocatépetl Volcano, México

A long-lived eruption of Popocatépetl volcano in central México has produced almost continuous ash fall on the populated areas for 30 years. The eruptive phase that began in 1994, has been characterized since 1996 by the growth of about 90 subsequent crater domes and their destruction that has produced most of the ongoing ash emissions. Since the beginning of the ash emission in 1994, we designed, established, and maintained an ash-sampling network of more than 200 sites around the volcano. This sampling network has been improved over the years and there are currently also 19 automated samplers, that we describe in this manuscript. This ash sampling network is part of the Popocatépetl monitoring system run by Universidad Nacional Autónoma de México (UNAM). The sampling sites that are distributed over an area of ∼8000 km² where ash fall occurs, involve collection of ash over 0.4 cm² and 1 m² areas during ash emission events associated with plumes over 1 km high. Community participation has greatly enhanced both, ash sample collection efficiency and public awareness.

Growth and destruction of lava domes are variable over time, with growth times that could last up to weeks and residence times ranging from days to months, producing frequent ash emissions. There have been about 1225 ash emissions >1 km high, of these, 110 have been identified with ash columns from 3 to 13 km high above the crater (8.5–18.5 km asl), some of which has produced abundant ash fall in nearby populations. Ashfall has been distributed in all directions around the volcano up to 2 50 km from the crater but dominantly in the east and northeast direction. The total minimum volume of non-compacted ash emitted over these three decades is >149 × 10⁶ m³ while the estimated total volume of lava emitted in the form of domes is >70 × 10⁶ m³.

The average ash mass load is 32 g/m² and the ash is commonly deposited <30 km from the crater and up to 250 g/m² have been deposited in periods of intense activity. Ash grainsizes range from coarse to extremely fine (MdPhi 1–6) with up to 37% of particles smaller than 10 μm and up to 10% smaller than 2.5 μm. Medium lapilli (MdPhi −3) was ejected during a sub Plinian event in 2001.

Ash emission is common in both dome growth and destruction phases, as well as in the clearing of the conduits during explosive phases in the absence of domes. Vitreous lithic fragments are produced by fragmentation of the degassed lava domes in the vent. Higher amounts of vesicular clasts, individual glass particles and crystals, on the other hand, are associated with magma ascent into a more open vent. The higher percentage of accidental lithic particles is linked to clearing of the vent.