Characteristics of the beginning of the 2019 eruptive crisis at Ubinas
volcano (Peru)
Abstract
Ubinas volcano has produced moderate explosive eruptions during the last
~500 years. With 26 eruptive periods, this composite
cone is the most active volcano in Peru. The 2006–2009 and 2013–2017
eruptions impacted people, agriculture, and livestock within 15 km of
the vent. On 24 June 2019 a new eruptive cycle started with minor
emissions of tephra and aerosols. Activity increased on July 19 with an
explosion beginning at 2:30 AM (local time). At that time, seismicity
also increased with a predominance of LP-type signals. Two clearly
differentiated and wind-controlled volcanic plumes were observed.
Initially, the plume reached 6500 m above the summit and the main
dispersion axis was ESE, dispersing ash as far as 300 km away to the
villages of Jesús de Machaca and Catacora, Bolivia, where ash fall
disrupted people’s daily activities. While the first plume was still
active, a 1200-m-high secondary plume developed and was dispersed to the
SE, reaching more than 200 km away into the Tacna region (Peru). After
July 19, the SO2 emission rate increased reaching 9600 TN/day on July
23. The tephra fall on July 19 and gas emissions forced Civil Defense
authorities to subsequently evacuate residents living in the valleys
around Ubinas within 15 km of the volcano. Just after the tephra fall on
July 19, deposit thickness was measured along the secondary dispersion
axis, where the nearest populated and most impacted areas are located.
The accumulation of lapilli and ash during the July 19 eruption reached
7 mm in the village of Ubinas, 5 mm in Tonohaya, 4 mm in San Miguel, 3
mm in Escacha and Huatagua, 2 mm in Huarina and 1 mm in Matalaque,
~20 km away. Fine ash accumulation was also reported at
the Quellaveco mine, 90 km to the SE. Samples collected at 3.2 and 6 km
from the vent allowed three types of juvenile clasts to be
differentiated; dark- and light-gray scoria and dense, dark-gray
lithics. Some juvenile clasts have bands of dark and light material,
suggesting a partial mixing (mingling) of compositionally different
magmas, which might have triggered the eruption. Based on the variety of
juvenile clasts and unprecedented SO2 emission rates compared to the two
past eruptive periods, we expect stronger eruptive activity or at least
a long-lasting eruptive cycle.