International Workshop on the mechanism of Phreatic Eruption

Persistently Restless Volcanoes: Insights from Telica Volcano, Nicaragua
Diana Roman1, Peter LaFemina2, Mel Rodgers3, Halldor Geirsson4
1) Carnegie Institution for Science, 2) The Pennsylvania State University, 3) University of South
Florida, 4) University of IcelandE-mail: droman(at)carnegiescience.edu
Many of Earths volcanoes experience well ‐defined states of “quiescence” and “unrest,” withunrest occasionally culminating in eruption. Some volcanoes, however, experience an unusuallyprotracted (i.e., decades‐long) period of noneruptive unrest and are thus categorized as“persistently restless volcanoes” (PRVs). The processes that drive persistently restless volcanism
are poorly understood, as our knowledge of PRVs is currently based on a small number of casestudies. Here we examine multidisciplinary observations of the 1999 (Rodgers et al., 2013), 2011
(Geirsson et al., 2014), and 2015 (Roman et al., 2019) phreatic eruptions at Telica Volcano,
Nicaragua, in the context of its long‐term behavior (Rodgers et al. 2015). We suggest that thelatter phases of the 2015 eruption were ultimately driven by destabilization of its shallow magmareservoir. Based on multiparameter observations at Telica over a 7‐year period, we propose thatthree distinct states of unrest occur at Telica over decadal timescales (Fig 1): a stable open state
involving steady conduit convection and two distinct “unstable” states that may lead to eruptions.
In the “weak sealing” state, phreatic explosions result from steady conduit convection underlying
a weak seal. In the “destabilized” state, destabilization of the top of the convecting magma in theconduit leads to rapid accumulation of high pressures leading to strong/impulsive
phreatomagmatic explosions. In contrast to “typical” precursory sequences, a decrease in lowfrequency seismicity rates occasionally accompanied or followed by an increase in highfrequency seismicity rates (consistent with a transition from open‐ to closed‐system behavior)appears to have been prognostic of phreatic eruption likelihood at Telica on both long (months) to
short (minutes) timescales. Our observations and interpretations suggest that continuous seismic,
ground‐based deformation, gas emission, and thermal monitoring and interpretation of thesedata within a paradigm of sustained conduit convection modulated by episodes of sealing anddestabilization of shallow magma reservoirs may allow robust forecasting of eruption potential,energy, and duration at Telica and similar PRVs worldwide.

International Workshop on the mechanism of Phreatic Eruption

Fig. 1. Conceptual model of “stable” and “unstable” states and transitional behavior at Telica andsimilar persistently restless volcanoes over multidecadal timescales. Telica cycles from an openstate through a sealed state leading to weak explosions. If the weak explosions are able to fully
break the seal and relieve accumulated pressure, the stable open state is reattained. If the weak
explosions are unable to fully relieve accumulated pressure, the shallow magmatic system isdestabilized, leading to rapid accumulation of pressure that leads to strong explosions. Thesystem then returns to a stable open state. HF = high frequency; LF = low frequency.
References
Rodgers M, Roman DC, Geirsson H, LaFemina P, Munoz A, Guzman C, Tenorio V (2013)
Seismicity accompanying the 1999 eruptive episodes at Telica Volcano, Nicaragua. Journalof Volcanology and Geothermal Research 265: 39-51.
Geirsson, H, Rodgers MJ, LaFemina P, Witter M, Roman DC, Munoz A, Tenorio V, Alvarez J,Conde Jacobo V, Nilsson D, Galle B, Feineman MD, Furman T, Morales A (2014).
Multidisciplinary observations of the 2011 explosive eruption of Telica volcano, Nicaragua:
Implications for the dynamics of low-explosivity ash eruptions. Journal of Volcanology andGeothermal Research 271: 55-69.
Rodgers MJ, Roman DC, Geirsson H, LaFemina P, McNutt SR, Muñoz A, Tenorio V. (2015) Stableand unstable phases of elevated seismic activity at the persistently restless Telica Volcano,Nicaragua. Journal of Volcanology and Geothermal Research 290: 63-74.
Roman DC, LaFemina PC, Bussard R, Stephens K, Wauthier C, Higgins, M, Feineman M,Arellano S, de Moor JM, Avard G, Martinez Cruz M, Burton M, Varnam M, Saballos A, Ibarra
M, Strauch W, Tenorio V (2019). Mechanisms of unrest and eruption at persistently restless
volcanoes: Insights from the 2015 eruption of Telica Volcano, Nicaragua. Geochemistry,Geophysics, Geosystems 20. https://doi.org/10.1029/2019GC008450