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Introducing Volcano Mombacho

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

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 Mombacho


Reason for Interest
Sometimes a volcano highlights a hazard which is not so obvious yet has clear evidence of the risks in its history. In this case the hazard is massive landslides and tsunamis within an inland lake. Whilst this volcano may not have much opportunity for further collapse there are other volcanoes nearby which pose a equal risk. This risk does not even require volcanic activity to be realized.

The Setting
Mombacho Volcano is in Nicaragua the largest country in the Central American isthmus, bordered by Honduras to the northwest, the Caribbean to the east, Costa Rica to the south, and the Pacific Ocean to the southwest. On the Pacific side of Nicaragua are the two largest fresh water lakes in Central America Lake Managua and Lake Nicaragua. 

The Pacific lowlands zone of Nicaragua has temperatures which remain virtually constant throughout the year, with highs ranging between 29.4 and 32.2 °C. After a dry season lasting from November to April, rains begin in May and continue to October, giving the Pacific lowlands 40 to 60 in of precipitation.  Punctuating this plain are several large volcanoes of the Cordillera Los Maribios mountain range, including Mombacho just outside Granada.

The North and Central highlands enjoys milder temperatures with daily highs of 23.9 to 26.7 °C. About a quarter of the country's agriculture takes place in this region, with coffee grown on the higher slopes. Oaks, pines, moss, ferns and orchids are abundant in the cloud forests of the region.

The sparsely populated Caribbean lowlands has large rain forests with the climate being predominantly tropical, with high temperature and high humidity. 



The Tectonic environment
The west coast of Nicaragua and Central America is a convergent margin where oceanic crust of the Cocos plate which is part of the Pacific Ocean plate is being subducted beneath the western edge of the Caribbean plate. A volcanic arc with active volcanoes, earthquakes, and steep mountains has formed above this convergent margin subduction zone. The Mombacho volcano stands on the Central American Volcanic Front which in Nicaragua aligns along the edge of the Nicaraguan depression.

The Nicaraguan depression which contains Lakes Nicaragua and Managua is a 100km wide depression extending 342 km across the length of Nicaragua. The exact reason for the depression is hotly contested but seems to be due partially to the plate convergence crumpling and partially due to subsidence of blocks of crust. It is argued that these blocks are twisting due to the angled convergence of the plates with the result that each block has compression and extension sections as it tries to rotate.



The Volcano
Mombacho is a 1345m High stratovolcano located 12km South of the city of Granada bounded by lake Nicaragua to the east and by Apoyo Caldera a few kilometers to the North West. Current activity consists of fumaroles and hot springs within the 2 collapse scarps and on the upper northern flank.  At least three large-volume debris avalanche deposits have been attributed to Mombacho and resulted from catastrophic flank collapse. 



The long runout of the northern deposit reached Lake Nicaragua and formed the peninsula and cluster of islands, Isletas de Granada 11 km NE from Mombacho's summit.


The northern landslide scar is shallow-rooted and cuts the volcano’s flanks down to the base and show little evidence of hydrothermal activity. This suggests the landslide is unlikely to have been caused by eruptive activity. Parts of the landslide include basement rocks suggesting the failure went down into the substrata. It has been proposed that this indicates spreading under this part of the volcano. Forest cover indicates the landslide is at least 1000 years old while underlying deposits suggest that it is  younger than 20000 years.



The southern landslide in contrast has a high content of extremely altered material provides evidence that the rock mass suffered intensive hydrothermal alteration before the collapse. Historical archives infer that the trigger to this avalanche may have been continuous swarms of seismic activity concluded by an earthquake in 1570. Accounts from the time suggest the 1570 debris flow at Mombacho was similar too the 1998 flow at Casita where intense rainfall triggered the landslide.


A third landslide deposit can be found south east of the volcano but is hidden by eruption deposits.

The lower two-thirds of this mountain is reserved for agriculture.  But higher up the peak the flora is a mix of dry forest and savannah trees with coffee plantations mixed in below the trees. At the highest levels are the cloud forest that form the nature reserve. The Mombacho Volcano Nature Reserve has a wide variety of trees and plants that thrive on the mountain due to the cloud forest’s humidity you can also observe howler and white face monkeys, snakes, deer, reptiles, birds and insects. There are several endemic species living on Mombacho including the Mombacho salamander. 





The Casita landslide

In late October and early November 1998 torrential rains of Hurricane Mitch caused numerous slope failures in Central America, the most catastrophic of which occurred at Casita volcano in Nicaragua. On October 30, 1998  residents south of the Casita volcano in Nicaragua heard a roaring noise like helicopters or thunder. Soon after a wave of muddy debris 1km wide and 3m deep roared down the Volcano destroyed all traces of two towns.  On the apron of the volcano where the flow spread out, survivors describe the flow as “an infernal wave of mud, rocks, and trees,”. The debris flow moved about 10 km from its source and generated floods that moved an additional 10 km downstream, destroying roads and bridges and inundating homes.

While the chance of a landslide towards the city of Granada is low with collapse to the north East already having occurred there is still a possibility of a slide into the lake on the East. Further down the lake is the Concepción Volcano which is constructed similarly yet with no slides so far. The risk of a lake tsunami seems possible and there is a large population within ones reach. At the very least it is worth highlighting a possibility.


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