Tephra Fall out and Lahar Flows in Concepcion Volcano Southwest Side of Lake Nicaragua

Introduction

Concepcion volcano is known for it has the highest summit mountain in Nicaragua and it lies on Mexico and central America. So far, many historical records have shown that it is still counted as an highly active volcano. According to Global Volcanism program last eruption was observed in 2011 which has series of explosive ash eruptions. Estimated in last 120 years, Concepcion has erupted more than 25 times.

It has very complicated geological structure. Since, consider its lithology like evolution of volcanic and tectonic; majority of rocks are comprise on basaltic andesite , andesite , basalt, pillow-basalt , basalt whereas minority of dacite is included.

Literature works which is about tephra and lahars asessment in the past seems quite beneficial but indexes are not clearly identified.

Methodology

In this study, assessment focuses mainly on tephra fallout frequency and their possible affect directions. Hazard information from last eruption 2010 – early 2011 and for the wind settlement databases from 2016 because this year has lots of available and consisting wind parameters. Whilst arranging tephra – ash fall out hazard , four session is considered as a function of specific equinox times in year.

First using Laharz to identify lahar flows and in total, with Madera volcano next to it, 9 lahars were drawn (Figure 1) by help of software programme. As mentioned before Concepcion volcano is situated on water, hence whole assuming lahar flows are limited with the boundary of sea levels. They are shown in the map in same colour (blue) to make it easier to map reader.

After that to create tephra fall out dispersals lines using TEPHRA2 and benefited from 2016 USGS wind database. Four months were taken into account to assume that each represent ideal solstice time of year. December datas were particularly used since that month`s wind indexes are more persistent and give very good range for tephra direction. As understood four (4) possible tephra fall out (Figure 2) ways were tried to draw and all indicates significancy levels of hazard from darker colours to slighter ones.

Errors and Uncertainties

First thing is whilst trying to calibrate exact coordinates on ArcGIS an error shows up about matching. Looing at previous studies then recognize there are lots of bulk density and gravity –jeodesy parameters on Concepcion volcano but lack enough and old to give evidence to follow appropriate hazard assessment.

Hazard Map

Basemap from the National Geographic World Map and main hazards map (Figure 2) scale is 1:500.000.

Hazar Level 1 -RED-

Relate to traffic light alert system city Altagracia, which is North-East of volcano, seems to be in danger for both lahar flow and bigger bulk of tephra accumulation. That might require to evacuation for people who residing there. To Bulletin reports for Concepcion volcano, high political (also social cost) risk might be considered near by the marine area and city`s own harbour.

Hazard level 2 -ORANGE-

Following the map and while tephra fall-out way across the lake, cities San Lorenzo and Camoapa respectively may be in less severe dangers. In a scenario during crisis; political risk level is slightly smaller than previous situation (before crisis). Activities for productivity in Chontales and Boaco might be affected by ash cloud propagation. In addition to this, relevant social impact could be harmful for fertilizer areas.

Hazard Level 3 & 4 -YELLOW AND GREEN-

In fact, rest of northside of Matagalpa seems not be in danger. Assuming that very little particles of tephra – ash fall out may drop there or no particules. Because wind affection is highly depends on variable changes ever year. Sufficient to say, some farmer properties and agriculture zones in north of Nicaragua would get deteriorate values. It can be said that a little bit of political attention up to local governments in Central America.

Discussions of Results

A small number of lahar flow affect residing places in both Concepcion and Madera volcanoes. In this study the important point is estimating right wind directions and thus feasible tephra – ash ways. It can inferred from the map that, none of airport around is affected by volcanic hazards. According to population density dots, in tephra fall out ways there seems no remarkable injure to human`s life.

References

https://volcano.si.edu/volcano.cfm?vn=344120

C. Scaini, A. Folch, M. Navarro, Tephra Hazard Assesment at Concepcion Volcano, Nicaragua, Journal of Volcanology and Geothermal Research volumes 219-220 pages 41-51, 2012

J. W. Vallance, S. P. Schilling, G. Devoli, M. M. Howell, Lahar Hazards at Concepcion Volcano, Nicaragua , 2001

R. Cioni, 2003 , The volcano – tectonic evolution of Concepcion, Nicaragua , Bulletin in Volcanology, May 2003

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