Source: Journal of Geophysical Research: Solid Earth
Hazardous pyroclastic density currents (PDCs) resulting from perched temporary tephra accumulations have been under-appreciated since the Fuego volcano (Guatemala) erupted on June 3, 2018. The unforeseen hazard, an approximately 12 kilometers long pyroclastic density current, happened about 1.5 hours after the eruption climax and destroyed the village of San Miguel de Los Lotes with hundreds of fatalities.
The concept of “perched temporary tephra storage” by Risica et al.  is based on information from satellite photos, deposit, and paleomagnetic analysis, which revealed that the PDC contained only 6% very hot (greater than 590 °C) clasts, 39% moderately hot (200-500 °C) clasts and 51% cool (less than 200 °C) clasts. These data clearly indicate that most deposits derived from the collapse of loose and partially hot material, stored over 2-3 years near the summit of the volcano, caused an unexpected block-and-ash flow with channel overspill and unexpected runout. With improved awareness of this phenomenon, new observatory monitoring practice and mitigation techniques can save lives.
Citation: Risica, G., Rosi, M., Pistolesi, M., Speranza, F., & Branney, M. J. (2022). Deposit-derived block-and-ash flows: The hazard posed by perched temporary tephra accumulations on volcanoes; 2018 Fuego disaster, Guatemala. Journal of Geophysical Research: Solid Earth, 127, e2021JB023699. https://doi.org/10.1029/2021JB023699
—Agnes Kontny, Associate Editor, Journal of Geophysical Research: Solid Earth