Contribution by Gino González Ilama, University of Costa Rica
Central America is home to more than 50 active volcanoes, with many large eruptions over the course of history. The volcanism in the region is widespread, including effusive, explosive and phreatic eruptions occurring today. The main source of volcanic eruptions in Central America is the subduction of the Cocos and Nazca plates beneath the Caribbean plate.
Momotombo volcano is located 40 km to the NW of Managua, the capital of Nicaragua. In 1609 this volcano was responsible for an important migration of civilians to Leon City, due to several events which affected the old town including earthquakes, ash fall and even lava flow.
After 110 years of silence, on December 1st, 2015, Momotombo volcano began to erupt again with large scale lava flow on the NE flank. Some of this lava flow was visible from Managua (about 40 km away on the other side of the Managua Lake).
With this in mind, we visited the volcano 12 days after the first event. Our purpose was to measure thermal anomalies with the FLIR camera (Forward Looking Infrared Camera), take samples of the lava flow and describe the event.
Figure 1. Location and tectonic context of Momotombo volcano. The area marked with MO denotes the location of the sampling site along the new lava flow.
The lava flow descended on the NE flank, partially over the lava flow of 1905. This flow traveled 2 km from the top, with a volume of lava flow around 6×106 m3. This flow was delimited by consolidated levées, denoted by the FLIR camera.
Figure 2. Eruptions and lava flows of Momotombo volcano. a) effusive eruption, December 3rd, 2015. Photo credit AP; b) Lava flows of 1905 and 2015; c) explosive eruption of February 21st, 2016. Photo credit Álvaro Sánchez.
Macroscopically, the rocks are porphyritic basalt-andesite, with olivine (5%) and plagioclase (35%), and 15% porous.
The type of the lava flow is aa and has two parts: upper part was rough and sharp, and the lower part was continues hot. Also, many features related with the movement of the flow and change in the velocity and topography can be observed at that time on the site.
With the Flir Camera we measured around 700 °C, principally in the pipes, with some minerals in the boundaries.
After the lava flow…
Now (February/March 2016), the Momotombo volcano has changed its behavior presenting episodes of explosive activity, and the big deal will be: Why has it changed from effusive to explosive? It is difficult to explain, but maybe this explosive activity is due to the formation of a plug in the conduit or a summit dome and this could have increase the gas pressure in the conduit (F. Lucchi, written communication).
Along with this change in the activity, hazards have also changed. This is because explosive activity is generating pyroclastic density currents, driving more than 2 km at times, and ash plumes of more than 2 km height.
In this perspective, Momotombo volcano is a good example of how volcanoes wake up, and how they can change activity and hazard with each eruption.
Figure 3. View of Momotombo volcano and pipes in the lava flow. a) View of Momotombo volcano; b) thermal image of Momotombo volcano, the hottest color is the levées; c) pipe in the lava flow; d) thermal image of the pipe in other hot points.
Figure 4. Lava flow of Momotombo volcano and different features: a) collecting samples in the MO point indicated in Fig.1; b) macroscopic texture of the rock sample; c) and d) different structures related with the lava flow movement.