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  • Location: Coventry,Warwickshire
  • Location: Coventry,Warwickshire

    Introduction
    My intention is to produce a series of articles (depending on interest) which introduces ideas about volcanic and earthquake activity. I want to go slightly off the beaten track to explore oddities, volcano hazards, analysis methods, Wonders and Mankind’s impacts. Keep in mind I am not expert (corrections gratefully received), but hopefully these will at least give a flavour of some different places in the world and provide a few minutes escape from people’s troubles.

    Introducing Volcano Cerro Machin
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    Reason for Interest
    Cerro Machin is not the highest volcano in the region nor does it have a reputation, yet is one of the most dangerous volcanoes in Columbia with a history of repeated VEI5 eruptions. It has created lahars that ran for 100km and pyrocrastic flows that ran for 8km with over 20,000 people living within an 8km radius. What does pique my interest is the new muon background radiation experiment across the volcano which should be able to map some of the internals of the volcano.

    The Setting

    Cerro Machin is situated close to the equator in the department of Tolima in Columbia. There are no seasons, but it does enjoy a variety of different temperatures. It has snowy summits more than 5,000 meters high with below freezing temperatures, and hotter zones in wide valleys lower than 400 meters above sea level that reach temperatures hotter than 40 degrees Celsius. The Tolima department includes a mountainous region occupied by the Cordillera Central, a plain, that corresponds to the valleys of the rivers Magdalena and Saldaña and the region to the southeast which forms the western slope of the Cordillera Oriental.

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    Famous regional dishes include the Tamal Tolimense which is a corn and yellow pea-based paste with pork, egg, chicken and vegetable filling, wrapped inside a plantain leaf. It is home to cotton top tamarins, sword billed hummingbirds, jaguars, capybara, Andean bears and glass frogs.

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    The nearest city Ibagué features a cool (due to altitude) tropical rainforest climate and is known as The Musical Capital of Colombia and America. The city does experience noticeably drier conditions during the months of January and July but has no true dry season month, as all twelve months see on average more than 60 mm (2.4 in) of precipitation. Temperatures are relatively consistent throughout the course of the year in Ibagué, with average high temperatures of about 28 degrees Celsius and average low temperatures of about 18 degrees Celsius.  The rapid expansion of coffee planting on the slopes above the city contributed to its growth, especially after 1890. The plain and the neighbouring valleys produce cacao, tobacco, rice, and sugarcane.

    The Tectonic Setting

    The Cerro Machin volcano tectonic province (SCVTP) is located on the axis of the central cordillera of Columbia. It is related to the subduction of the Nazca Plate underneath the South American Plate. The SCVTP host 10 polygenetic volcanoes including Cerro Machin.

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    The Volcano

    The Cerro Machín a rhyolitic stratovolcano is located in the Central Cordillera of Colombia and is the lowest altitude volcano in Colombia (2750 m). Given the chemical composition, magnitude and extent of past eruptions, it is recognized as a explosive volcano with potential for damage to the local region for an extensive period. Cerro Machin volcano is located 150 km southwest of Bogota, 17 km west of Ibague, 30 km east of the city of Armenia on the eastern slopes of the Cordillera Central. Cerro Machin is in a warm temperate region with an mean temperature of 20°C, annual rainfall of 1150 mm, the average relative humidity is 85%, the dry and rainy seasons usually alternate during year.

    Cerro Machin has a 3km wide caldera breached to the south and contains three forested dacitic lava domes with fumarole activity and hot springs. Around the base of the domes to the south is a crescent shaped small lake. Columbia's national tree the wax palm covers much of the slopes up to the summit. In past eruptions pyroclastic flows traveled up to 40 km. The entire surface is covered by small tributaries of the Magdalena, the most important river of Colombia. It flows in a wide valley between the Cordillera Central and Eastern Colombian Andes.

    934759645_waxpalms.thumb.jpg.7ec8c83481201b5240e44d83ed674f1a.jpg

    Muography or muon tomography is a technique which uses atmospheric muons to study geological structures. The most common tools for studying volcanoes is gravimetry and electrical tomography which lack spatial resolution. MuTe is a hybrid detector composed of two sub dectectors,a hodosco9e and water cherenkov detector. One prototype has been deployed to Cerro Machin dome to understand the volcano structure.

    Historic Eruptions
    The volcano has had  6 main eruptive cycles occurring over the last 10k years with the biggest eruption of Cerro Machin is thought to have occurred 3600 years ago. The last known eruption at Cerro Machín Volcano in the Central Cordillera of Colombia occurred ∼900 years BP and ended with the formation of a dacitic lava dome. It has been determined that during it’s previous eruptions it produced pyroclastic flows that traveled as far as 40 km from the volcano and mud flow deposits (lahars) up to 109 km distance from the volcano along the Coello and Magdalena rivers. Beyond this basic information there is very little information available about previous eruptions.


    Recent Activity

    In April 2004, a swarm of earthquakes occurred at Machín volcano. More than 60 earthquakes occurred daily, in comparison to the normal number of 1-10 quakes. 

    An earthquake swarm occurred at Machín volcano on 9 November 2008. The increase in earthquakes was accompanied by an increase in fumarolic activity and there was damage to some buildings

    During December 2010 the number of earthquakes increased at Machin volcano. About 367 volcano tectonic earthquakes were recorded south and southwest of the main lava dome in the summit caldera in an area known as Moral, four to five kilometers deep. The largest event occurred at 5:22 pm on 1 January 2011, with a magnitude 2.3 at a depth of 3.3 km. The earthquake was felt by residents in vicinity of the volcano and in the town of Cajamarca (Tolima).

    An earthquake swarm occurred at Machín volcano on 9 November 2008. The increase in earthquakes was accompanied by an increase in fumarolic activity and there was damage to some buildings (USGS / GVP weekly reports).

    During 2020 the Servicio Geológico Colombiano recorded that the seismic activity continues at elevated levels. Most seismic activity has been associated with rock fracturing. The seismic station records earthquakes at 2.4-7.8 km depth beneath the south and southeast flank. On 6 May at 00:34 local time SGC detected an earthquake located 1.1 km southeast of the dome at 2.3 km depth.


    Discussion

    Cerro Machin would not immediately threaten major cities even though they are not far away but can have major impacts on trade and a significant number of people close by. In addition, a major transport route from Bogota to the Pacific (Route 50) could be affected. The major threat is to local agriculture particularly coffee bean growing. What surprises me is the general lack of information about one of the most dangerous volcanoes in Columbia despite quite technologically advanced monitoring.
     

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