Rincón de la Vieja is a remote volcanic complex in the Guanacaste Range in NW Costa Rica. It consists of an elongated, arcuate NW-SE-trending ridge constructed within the 15-km-wide Guachipelín caldera, whose rim is exposed on the south side. Eruptions dating back to the 16th century have been from the active crater located ENE of Von Seebach crater; the active crater also contains a 500-m-wide acid lake. The current eruption period began June 2021 and has more recently consisted of weak phreatic explosions (BGVN 48:01). This report covers activity during January through June 2023 using information from weekly bulletins and occasional daily reports from the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA).

Activity was relatively low during January through February 2023. An eruption was reported at 1500 on 7 January, followed by observations of gray water in the Niño River. According to OVSICORI-UNA, these observations may have indicated that some material from the eruption came out of the crater. During 0537-0547 on 8 January a series of eruptions was detected.

On 2 March at 0651 and on 4 March weak gas-and-steam emissions were recorded, rising less than 500 m above the crater. A series of small eruptions occurred during 2305 on 10 March to 0137 on 11 March with at least four pulses confirmed in webcam images at 2305, 0000, 0006, and 0137. Continuous tremor was reported on 11 March. Weak gas-and-steam plumes sometimes rose higher than 500 m above the crater, but no ash was visible. Two eruptions were detected at 0529 and 0549 on 14 March, which generated a gas-and-steam plume that rose 2 km above the crater and drifted W and NW (figure 38). On 19 March at 1051 small gas-and-steam emissions rose less than 500 m above the crater.

Figure 38. Photo of a white gas-and-steam plume rising 2 km above the crater rim of Rincón de la Vieja on 14 March 2023. Courtesy of OVSICORI-UNA.

Tremor was reported starting around 2230 on 10 April. A small phreatic eruption was reported on 11 April; several pulses occurred between 0653 and 0700, the largest of which was recorded at 0656. A resulting gas-and-steam plume rose 500 m above the crater. Another gas-and-steam plume was recorded at 0743; tremor decreased in amplitude after 0900. Two small eruptions were recorded during the night and early morning during 11-12 April; the strongest of which occurred at 0450 and generated a gas-and-steam plume that rose 500 m above the crater and drifted SW. Two more eruptions were detected at 1920 on 12 April and at 0632 on 13 April; gas-and-steam plumes accompanied these events, but no ash was observed. On 14 April at 0455 low-frequency earthquakes were detected and an eruption was reported at 0935 that continued until after 2100; the resulting gas-and-steam plume rose 2 km above the crater and drifted SW. Another eruption was detected at 1826 on 14 April. On 16 April a small eruption was recorded at 0647 and lasted approximately one minute and generated a small lahar in the upper part of the basin. An accompanying gas-and-steam plume rose 2 km above the summit (figure 39). Another eruptive event occurred at 0957 and produced a gas-and-steam plume that rose 500 m above the summit. On 19 April several eruptions generating gas-and-steam plumes were reported, which rose as high as 1.5 km above the crater and drifting W. On 21 April at 1550 a strong eruption was reported. The accompanying gas-and-steam plume rose 4-5 km above the crater and drifted SW (figure 40). Lahars were observed on the N flank. Continuous degassing was reported after this eruption event, as well as strong tremor. On 21 April at 1904 a small eruption was detected in infrasound and seismic records. Near-continuous degassing persisted in the crater. On 22 April at 1904 a small eruption was detected in infrasound and seismic records and near-continuous degassing was observed in the crater. Three gas-and-steam emissions were detected on 26 April at 0453, 0523, and 0545. An eruption event at 0528 on 27 April generated a gas-and-steam plume that rose 800 m above the crater. A small eruption at 1030 on 30 April produced a gas-and-steam plume that rose 500 m above the crater accompanied by a near-continuous tremor. Several volcano-tectonic (VT) earthquakes were also detected both distally and proximally to the crater.

Figure 39. Photo of an eruption at Rincón de la Vieja at 0647 on 16 April 2023 that generated a white gas-and-steam plume and a small lahar in the upper part of the basin. Courtesy of OVSICORI-UNA.

Figure 40. Photo of the strong eruption at 1550 on 21 April 2023. The accompanying gas-and-steam plume rose 4-5 km above the crater and drifted SW. Courtesy of OVSICORI-UNA.

A moderate phreatic eruption was recorded at 1306 on 1 May that generated a gas-and-steam plume that rose 1 km above the crater. Residents to the N, seismographs, infrasound systems, and webcams all recorded the event. Seismographs recorded intermittent volcanic tremor signal and several VT-type earthquakes were recorded both distally and proximally to the crater. A small phreatic eruption was recorded at 1847 on 5 May based on data from seismographs and the infrasound system. Intermittent volcanic tremor and several low-frequency volcanic earthquakes were also detected. A short-lived explosive and energetic eruption was detected at 0258 on 14 May that produced lahars that flowed down the Pénjamo River, the Azul River, and the Azufrado River. Volcanic tremor decreased substantially on 13 May, though continuous degassing was reported. On 17 May four small phreatic eruptions were recorded, one of which occurred at 1255 that generated a gas-and-steam plume that rose 700 m above the crater. Gas-and-steam emissions persisted from the Main Crater and intermittent volcanic tremor were recorded. A gas-and-steam plume was detected in webcam, infrasound, and seismic data at 1349 on 22 May that rose 1 km above the crater. A gas-and-steam plume rose 2.5 km above the crater at 1815 on 24 May possibly containing some material from the lake.

Two moderate phreatic eruptions were detected at 1815 and 1830 on 24 May that produced gas-and-steam plumes and rose 2.5 km above the crater. The eruptions were detected by residents to the N, seismographs, the infrasound system, and webcams. Intermittent volcanic tremor was also recorded. Aerial photographs taken from 24 May showed a low water level in the lake of the Main Crater and that the lake was milky gray in color. The surface around the crater was covered in recently erupted white ash deposits (figure 41). Intermittent eruptions were reported during 25-26 May at 1435, 2230, 0453, and 0704, the strongest of which occurred at 1435. Small, low-frequency volcanic earthquakes and VT-type events proximal to the crater continued, but in smaller numbers. Intermittent degassing has persisted and there was a notable decrease in the lake level. Several eruptions were detected at 1357, 2248, and 2348 on 26 May and at 0221 and 0632 on 27 May. An eruption at 2135 on 27 May ejected incandescent material above the crater and generated a significant lahar on the N flank of the volcano that descended the Pénjamo River. The resulting gas-and-steam plume exceeded the field of view of the webcam, so OVSICORI-UNA estimated that it reached at least 3.5 km above the crater, and possibly as high as 4 km above the crater. On 29 May an eruption was observed at 0244 that ejected incandescent material and generated a lahar on the N flank of the volcano that descended the Pénjamo River.

Figure 41. Aerial photo of the Main Crater of Rincón de la Vieja taken on 24 May 2023. The active crater is covered in white ash deposits from recent eruptions. Courtesy of OVSICORI-UNA.

During 1-2 June five moderate phreatic eruptions were detected, the most energetic of which occurred at 0902 on 2 June. An accompanying gas-and-steam plume rose 1.5 km above the crater (figure 42). Seismographs intermittently recorded volcanic tremors. According to the Sentinel satellite, a sulfur dioxide plume weighing 37 tons was recorded on 2 June that drifted E. On 3 June at 0624 a gas-and-steam plume rose 1.5 km above the crater and drifted W. Some low magnitude VT-type events were recorded S of the Pailas area of the Rincón de la Vieja Volcano National Park. Sulfur dioxide emissions were recorded at average values of less than 300 tons/day. On 4 June at 0526 an eruptive plume reached 500 m above the crater, accompanied by a vertical gas-and-steam plume that rose 3.5 km above the crater and drifted N. OVSICORI-UNA reported that ash remained in the crater and there were no reports of it falling outside the summit. An eruption was recorded at 1804 on 5 June generated a gas-and-steam plume that rose 1 km above the crater, based on data from webcams, seismographs, infrasound sensors, and ground observations made to the N of the volcano. On 6 June at 0259 a small phreatic eruption was recorded that produced a gas-and-steam plume 3 km above the crater and drifted NW. On 7 June at 0142 a small eruption lasted 14 minutes based on webcam images. The eruption consisted of two pulses, the second of which was slightly more energetic. One eruption was recorded at 1505 on 7 June, but due to weather conditions the height of the plume could not be observed. Another eruption at 0942 on 8 June generated a gas-and-steam plume that rose 2.5 km above the crater. A moderate phreatic eruption was recorded at 1810 on 8 June that ejected lake water with sediment to less than 100 m above the crater rim; the accompanying white gas-and-steam plume rose 3 km above the crater and drifted W. Small phreatic eruptions were recorded at 0357, 0521 and 0546 on 11 June, the latter two of which produced a white gas-and-steam plume that rose 1.5 km and 2.5 km above the crater, respectively and drifted W. On 18 June small eruptions were recorded at 0440 and 0904 and continuous degassing was observed. A small phreatic eruption at 1804 on 18 June generated a gas-and-steam plume that rose 2 km above the crater. Several small, low-energy eruptions were recorded during the night of 25-26 June, the last one of which was recorded at 0547 that generated a gas-and-steam plume that rose 1.5 km above the crater.

Figure 42. Image showing a white gas-and-steam plume rising 1.5 km above the crater of Rincón de la Vieja at 1907 on 2 June 2023. Courtesy of Carol Quesada via OVSICORI-UNA.

Geological Summary. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/, https://www.facebook.com/OVSICORI/).