The Instituto Geofísico (IG-EPN) was created in 1983 by faculty of the Escuela Politécnica Nacional, a public university in Quito, Ecuador, with the objective of assessing volcanic hazard in the country. Since then, the IG-EPN has established and developed an instrumental monitoring network and from 1999 has faced the eruption of five continental-arc volcanoes (Guagua Pichincha, Tungurahua, Reventador, Cotopaxi, and Sangay) which displayed varied hazards, eruptive dynamics, eruption durations, and socio-economic contexts. At the same time, mainly effusive eruptions took place in Galápagos archipelago, which has undergone an increase in local population over the last two decades and hence in the risk posed by volcanic eruptions. The outstanding handling of these volcanic crises was the reason why IG-EPN was granted with the 2020 Volcanic Surveillance and Crisis Management IAVCEI Award. Now, the IG-EPN manages a country-wide network of about 500 instruments to monitor both volcanic and tectonic activity with a highly qualified staff of 80 people. This manuscript describes the history of IG-EPN, the main volcanic hazard studies and resulting hazard maps; the instrumental networks; and the volcanic crises that the IG-EPN faced during the last forty years.

Northwestern South America is a plate boundary zone where the Nazca, Caribbean and South American plates interact to produce a wide area of active continental deformation from the Gulf of Guayaquil (latitude 3○S) to Venezuela. Previous studies have identified a ∼2000 km long continental sliver, referred as the North Andean Sliver (NAS), squeezed between the Nazca, Caribbean, and South American plates, and escaping at ∼1 cm/yr northeastward with respect to South America. Subduction of the Nazca plate beneath the NAS has produced a sequence of large and great earthquakes during the 20th century along the coast of Ecuador and Colombia. Large crustal earthquakes up to magnitude 7.7 have been documented along the proposed eastern boundary of the NAS. However, active tectonics data, historical and recent earthquakes all indicate active fault systems within the NAS, possibly resulting from the interaction of several tectonic blocks. Here, we derive an extensive horizontal velocity field using continuous and episodic GNSS data from 1994 to 2019.9, covering northern Peru, Ecuador, Colombia, Panama and Venezuela. We model the GNSS velocity field using a kinematic elastic block approach that simultaneously solves for rigid tectonic block rotations and interseismic coupling along the subduction interfaces and along major crustal faults. In contrast to previous results that considered a single rigid NAS, our dense GNSS velocity field demonstrates that the NAS undergoes significant internal deformation and cannot be modeled as single rigid block. We find that block kinematics in the northern Andes are well described by the rotation of 6 tectonic blocks, showing increasing eastward motion from south to north. The Eastern boundary of the sliver is defined by a right-lateral transpressive fault system accommodating 5.6 to 17 mm/yr of motion. Fragmentation of the NAS occurs through several fault systems with slip rates of 2-4 mm/yr. Slow reverse motion is found across the sub-Andean domain in Ecuador and northern Peru at 2-4 mm/yr, marking a transitional area between the NAS and stable South America. In contrast, such a transitional sub-Andean domain does not exist in Colombia and western Venezuela. At the northwestern corner of Colombia, fast (∼15 mm/yr) eastward motion of the Panama block with respect to the NAS results in arc-continent collision. We propose that the Uramita fault and Eastern Panama Deformed Zone define the current Panama/NAS boundary, accommodating 6 and 15 mm/yr of relative motion, respectively. A fraction of the Panama motion appears to transfer northeastward throughout the San Jacinto fold belt and as far east as longitude ∼75○W. Along the Caribbean coast, our model confirms, slow active subduction at ∼4.5 mm/yr along the South Caribbean Deformed Belt offshore northern Colombia and a relatively uniform rate of ∼1-2 mm/yr offshore northern Venezuela. Along the Nazca/NAS subduction interface, interseismic coupling shows a first-order correlations between highly locked patches and large past earthquake ruptures. These patches are separated by narrow zones of low/partial coupling where aseismic transients are observed. Compared to previous studies, our interseismic coupling model highlights the presence of deep coupling down to 70 km in Ecuador.

The youngest volcanism of the Ecuadorian Volcanic Front (Western Cordillera) is mainly dominated by highly explosive events, including the growth and violent destruction of lava domes, and the formation of thick pyroclastic sequences. Deposits associated with such eruptive dynamics have been identified at Iliniza, a compound volcano located in the Western Cordillera with a poorly defined evolutionary history. We present the first K-Ar ages of Iliniza volcano combined with stratigraphic data, numerical reconstructions, and geochemical analyses, providing a new perspective on its evolution. Our results show that Iliniza volcano is much younger than previously proposed. The Iliniza twin-peaked shape is the result of the superposition of two andesitic to dacitic stratovolcanoes. (1) The North Iliniza (NI) edifice was constructed by two lava successions and an intermediate satellite vent, showing a short range of mainly effusive activity between 123 ± 6 and 116 ± 2 ka. (2) The South Iliniza (SI) edifice began its construction through the Lower SI stage when massive lavas dated at ~45 ka formed a basal cone. During the Upper SI stage, the uppermost part of this edifice was destroyed by the highly explosive Jatuncama phase (VEI 5) leaving a 30–40 m-thick ignimbrite sequence. The subsequent extrusion of several dacitic lava domes reconstructed the South Iliniza summit at around 35 ka. The Terminal SI stage corresponds to the emission of several andesitic lavas between 31 ± 4 and 25 ± 3 ka. The Iliniza eruptive activity extended into the Late Pleistocene and Holocene with the extrusion of the Tishigcuchi lava dome, and the emission of the Pongo lava flow dated at 6 ± 4 ka. Based on the proposed eruptive history, we suggest that a revised volcanic hazard assessment of the potentially active Iliniza volcano is required.

Sumaco is a stratovolcano located in the northern SubAndean zone of Ecuador, 105 km east of Quito. The flanks of Sumaco are jungle-covered, and scarce outcrops are found along stream banks, trails and, in quarries. Based on our field studies, eruptions of Sumaco during the historical era were associated with small-scale Strombolian activity. Earlier more robust activity, which pertains to the last 4400 years, had vigorous eruptions whose ∼10 cm thickness ash fallout deposits are identified more than 20 km from the vent. Stratigraphic sections studied around the volcano's outer flanks identify five principal ash-fall layers corresponding to Sumaco's activity. The ash layers contain white micro-vesiculated pumice, displaying clinopyroxene, plagioclase, traces of amphibole, and biotite crystals. Also, gray lithics with pyroxene phenocrysts and scarce plagioclase crystals are present. The amount of volcanic glass shards is meager in almost all samples. The thickest ash layer, “SUM-JS-44″, was dated by ¹⁴C, obtaining an age of 3029-2888cal AD. Analysis of a sediment core obtained from the “Guagua Sumaco” near-source lagoon allowed us to identify nine ash layers; seven are from Sumaco. Dating an underlying layer of peat (OL3) beneath the six ash layers provides an age of 1483–1644 cal AD, showing that Sumaco volcano experienced at least six separate eruptive pulses during the last centuries, and thus it should be considered potentially active. Based on morphological observations, Sumaco's edifice consists of three phases: PaleoSumaco, Recent Sumaco, and Current Sumaco, differentiated mainly by two scars representing flank collapses that produced far-reaching debris avalanches, whose breccia deposits are observed around the cone's depositional apron. The aim of our research is to understand the evolution of Sumaco's edifice and verify the relative youthfulness of the volcano and its eruption styles. These inputs are then applied in determining three eruption scenarios.