In the middle of an apparent lull in eye-catching activity elsewhere, our interest has been focused on two Central American volcanoes recently that both bear keeping an eye upon for different reasons. Colima has been active since 2013 and is the most active volcano in Mexico. It is covered by a couple of very good webcams that regularly offer interesting views of Strombolian to Vulcanian blasts, day as well as night. In contrast, Momotombo had been inactive for a century before it sprang back to activity last year. While it too is covered by webcams, the instrumentation available courtesy of Ineter (Instituto Nicaragüense de Estudios Territoriales) is quite comprehensive even if what they reveal is baffling.
Volcan de Colima
Also known as Volcán Fuego (fire) or sometimes as Colima de Fuego, the Colima volcanic complex is located in the western part of the Mexican Volcanic Belt. It consists of two major peaks; to the north, the older Nevado de Colima (4320 m a.s.l.) and to the south, the younger Volcán de Colima (3850 m a.s.l.) with a third, the oldest and eroded El Cantaro, being considered extinct. The Fuego edifice stands in a 5-km wide caldera that is breached to the SSW in the direction of the town of Colima City (pop. 132,273 as of 2005), 30 km from the volcano. There is also a parasitic set of domes known as El Volcancito on the northeast flank of Fuego. In addition, the complex is spanned by a group or groups of cinder cones which date back more than 10,000 years.
The Colima volcanic complex has an estimated volume in excess of 700 km3, which makes it twice as large as the Mount Shasta complex in California. It is situated on the Colima graben and as with the Popocatepetl group of volcanoes, the source of the magma is a steeply inclined subducting plate, the subduction of which causes the volcanic centre to move from north to south with time.
While Nevado has not been historically active, that is there has been no observed eruptions since the arrival of the Spanish in the second decade of the 16th Century, Fuego is listed as having had 57 eruptions or eruptive periods since the first registered in 1519. Colima de Fuego erupts with Strombolian to Vulcanian explosions and while there is one VEI 5 listed (1913) as well as a handful of VEI 4, the median eruption is VEI 2 and the erupted lavas andesitic to basaltic-andesitic in the main. The previous eruptive cycle (1997-2011) left the crater plugged by a dome which was destroyed as the ongoing cycle commenced.
The main hazard associated with frequent but small explosive eruptions that showers the flanks with picturesque cinders is that welding is poor. This means that the Colima volcanic complex is little more than an immense pile of rubble and prone to both flank collapses and lahars. There is evidence of repeated, major slope failures from both cones which have left a thick blanket of debris on the E, S and W sides. The largest identified such collapse occurred in the late Pleistocene reaching the Pacific 120 km away and covered some 2,200 km² with approximately 25 km³ of avalanche debris. As more than 300,000 people live within 40 km of the Colima complex, it is not surprising that it was designated as one of the 16 Decade Volcanoes.
At present, eruptions at Colima are ongoing and there is a very high probability of catching one in the act whatever the time of day on one of the excellent webcams provided by Webcams de Mexico.
Located immediately adjacent to Lago Xolotlán, Lake Managua, about 35 km NW of Managua, the picturesquely symmetrical cone of Momotombo is one of the major landmarks of Nicaragua and is part of the highly active Nicaragua-Costa Rica Quaternary volcanic chain. Apart from the main edifice, there is a highly active geothermal field on its SE flank and 10 km from its summit, the cone of Momotombito penetrates the waters to form a perfect miniature of its larger parent.
Momotombo is a very young, andesitic stratovolcano that is considered to be a Somma-volcano as it is centered on the southern rim of the by now almost in-filled caldera of the previous summit, Monte Galán. The current edifice began to grow as recently as 4½ thousand years ago and by now has an elevation of 1,297 m with a prominence almost as great. The volume of the new edifice is on the order of five cubic kilometres which yields a figure of approximately 1 km3 per 1,000 years. The erupted lavas are Andesite – Basaltic Andesite and Basalt – Picro-Basalt in composition.
Since the Spanish arrived in the first decade of the 16th Century, Momotombo has erupted fifteen times, almost always a VEI 2 even if the first eruption in 1524 was a VEI 3 and a VEI 4 is listed as having taken place in 1605. Before the latest eruptive cycle began on Dec 1st 2015, Momotombo’s last confirmed eruption was in 1905 when a lava flow travelled down the NNE flank into the Galàn caldera, the same route taken by recent lava flows. Even if the cycle officially ended on April 7th 2016, the volcano has been at a high state of unrest since with copious amounts of water vapour being ejected in plumes several kilometres high at times.
As it stands on a highly active subduction zone, earthquake activity is high and it is not always easy to differentiate whether or not such swarms are merely tectonic or volcano-tectonic in nature. The information given by the excellent instrumentation provided by Ineter is also hard to unravel. After a particularly intense series of tremor including explosions, tornillos and harmonic tremor the other day, Carl Rehnberg said that any sane volcano would have erupted months ago.
As can be inferred, we at Volcanocafé would not be surprised if Momotombo suddenly returned to erupting at any moment. If so the action can be observed on the excellent instrumentation provided by INETER:
(MOM1 EHZ NU is recommended)
(MOM3 EHZ NU)