remote sensing Article Determination of Primary and Secondary Lahar Flow Paths of the Fuego Volcano (Guatemala) Using Morphometric Parameters Marcelo Cando-Jácome and Antonio Martínez-Graña * Geology Department, External Geodynamics Area, Faculty of Sciences, University of Salamanca, Plaza Merced s/n, 37008 Salamanca, Spain; [email protected] * Correspondence: [email protected]; Tel.: +34-923-294496; Fax: +34-923-923294514 Received: 2 February 2019; Accepted: 25 March 2019; Published: 26 March 2019 Abstract: On 3 June 2018, a strong eruption of the Fuego volcano in Guatemala produced a dense cloud of 10-km-high volcanic ash and destructive pyroclastic flows that caused nearly 200 deaths and huge economic losses in the region. Subsequently, due to heavy rains, destructive secondary lahars were produced, which were not plotted on the hazard maps using the LAHAR Z software. In this work we propose to complement the mapping of this type of lahars using remote-sensing (Differential Interferometry, DINSAR) in Sentinel images 1A and 2A, to locate areas of deformation of the relief on the flanks of the volcano, areas that are possibly origin of these lahars. To determine the trajectory of the lahars, parameters and morphological indices were analyzed with the software System for Automated Geoscientific Analysis (SAGA). The parameters and morphological indices used were the accumulation of flow (FCC), the topographic wetness index (TWI), the length-magnitude factor of the slope (LS). Finally, a slope stability analysis was performed using the Shallow Landslide Susceptibility software (SHALSTAB) based on the Mohr–Coulomb theory and its parameters: internal soil saturation degree and effective precipitation, parameters required to destabilize a hillside. In this case, the application of this complementary methodology provided a more accurate response of the areas destroyed by primary and secondary lahars in the vicinity of the volcano. Keywords: volcano deformation; lahars hazard; magma accumulation; pyroclastic flows; ash plumes 1. Introduction Primary lahars are flows which are formed as a direct result of a volcanic eruption. They tend to be bulky (107–109 m3) and record high speeds (>20 m/s). Their maximum flows are commonly between 103–105 m3/s. These features provide the ability to flow long distances, even hundreds of kilometers downstream. They occur primarily when during an eruptive event incandescent material causes the fast melting of large volumes of ice and snow of the glaciers that cover some volcanic edifices and flows by descent gullies. Secondary lahars mainly include lahars caused by the rains. The unbound, by previous eruptions, pyroclastic material can be easily removed by the rains. In general, these are at lower speed, volume and they travel shorter distances as compared to primary lahars, however, they are most frequent during periods of rain [1]. Guatemala is the only country in the Central American region that has trained local observers to generate reports on volcanic activity, who then transmit the information via radio and/or telephone three times a day. The information is transmitted to the National Institute of Seismology, Volcanology, Meteorology and Hydrology (INSIVUMEH) plant when the following characteristics are present: changes in the release of energy, increase in the number of explosions, increase in the expulsion of ash, increase in seismic activity, rumblings, shock waves, and the manifestation of block avalanches that descend through the ravines in the volcanic perimeter. Remote Sens. 2019, 11, 727; doi:10.3390/rs11060727 www.mdpi.com/journal/remotesensing Remote Sens. 2019, 10, x FOR PEER REVIEW 2 of 23 43 expulsion of ash, increase in seismic activity, rumblings, shock waves, and the manifestation of block 44 avalanches that descend through the ravines in the volcanic perimeter. 45 On 3 June 2018, a strong eruption of the Fuego volcano in Guatemala produced a dense volcanic 46 ash cloud rising to 10 km high. Following the collapse of the volcanic column, pyroclastic flows and 47 descending lahars caused significant damage and a high number of fatalities around the mountain Remote Sens. 2019, 11, 727 2 of 20 48 [2]. After the eruption, INSIVUMEH, with support from the Volcano Disaster Assistance Program 49 (VDAP) of the United States Geological Survey (USGS), the University of Edinburgh, and Michigan 50 TechnologicalOn 3 June University, 2018, a strong elaborated eruption 2 scenarios of the Fuegoof lahars volcano for medium in Guatemala and heavy produced rains based a denseon the 51 volcanicnumerical ash models cloud risingobtained to 10from km the high. program Following LAHAR the collapseZ (Figure of 1). the These volcanic scenarios column, can pyroclastic be seen on 52 flowsthe MapAction and descending page [3]. lahars caused significant damage and a high number of fatalities around the 53 mountainOn 19 [2 November]. After the and eruption, for the INSIVUMEH, fifth time during with 2018, support the fromFuego the volcano Volcano erupted, Disaster with Assistance a 1,200- 54 Programmeter long (VDAP) lava flow of the that United descended States Geologicalinto the Ceniza Survey canyon. (USGS), This the volcanic University flow of with Edinburgh, fragments and of 55 Michiganrock producws Technological by erosion University, on the slopes elaborated of the 2volcano scenarios moved of lahars downhill, for medium incorporating and heavy enough rains basedwater, 56 onso thethat numerical they formed models mud obtained flows and from volcanic the program debris or LAHAR lahars Zthat (Figure descended1). These the scenarios slopes of canthe bevolcano, seen 57 onaffecting the MapAction sectors such page [as3]. Las Lajas, El Jute, besides the Ceniza and Seca ravines, according to 58 INSIVUMEH in its last special volcanological bulletins (Nos. 157-2018 and 158-2018) [4,5]. 59 60 61 FigureFigure 1. 1.Web Web Map Map prepared prepared by by MapAction MapAction as as a collaboratora collaborator on on the the HazMap HazMap project project and and in supportin support of 62 Nationalof National Institute Institute of Seismology, of Seismology, Volcanology, Volcanolo Meteorologygy, Meteorology and Hydrology and Hydrology (INSIVUMEH). (INSIVUMEH). Data from Data 63 preliminaryfrom preliminary maps ofmaps the of hazard the hazard of pyroclastic of pyroclastic flows flows and lahars and lahars for scenario for scenario A (moderate A (moderate rainfall) rainfall) and 64 scenarioand scenario B (very B heavy(very rainfall).heavy rainfall). Prepared Prepared in June 2018in June by INSIVUMEH, 2018 by INSIVUMEH, Volcano Disaster Volcano Assistance Disaster Program (VDAP), United States Geological Survey (USGS), the University of Edinburgh, and Michigan 65 Assistance Program (VDAP), United States Geological Survey (USGS), the University of Edinburgh, Technological University. In C, location of Las Lajas, El Jute, Ceniza and Seca ravines. 66 and Michigan Technological University. In C, location of Las Lajas, El Jute, Ceniza and Seca ravines. On 19 November and for the fifth time during 2018, the Fuego volcano erupted, with a 1200-m 67 The theory of LAHAR Z’s operation will not be studied in this article, since it is not the objective long lava flow that descended into the Ceniza canyon. This volcanic flow with fragments of rock 68 of this study. Its operation is reviewed briefly. In this article, reference is made to the LAHAR Z producws by erosion on the slopes of the volcano moved downhill, incorporating enough water, so that 69 program and its results as a basis for superimposing the results obtained by the Differential they formed mud flows and volcanic debris or lahars that descended the slopes of the volcano, affecting sectors such as Las Lajas, El Jute, besides the Ceniza and Seca ravines, according to INSIVUMEH in its last special volcanological bulletins (Nos. 157-2018 and 158-2018) [4,5]. The theory of LAHAR Z’s operation will not be studied in this article, since it is not the objective of this study. Its operation is reviewed briefly. In this article, reference is made to the LAHAR Z program and its results as a basis for superimposing the results obtained by the Differential Interferometry Remote Sens. 2019, 10, x FOR PEER REVIEW 3 of 23 70 Interferometry Synthetic Aperture Radar Differential (DINSAR) analysis, the morphometric indices Remote Sens. 2019, 11, 727 3 of 20 71 and the unstable areas near the volcano. 72 LAHAR Z was written to delimit areas of potential lahar inundation from one or more user- 73Synthetic specified Aperture lahar Radarvolumes. Differential LAHAR (DINSAR)Z is a code analysis,that is executed the morphometric within a geographic indices and information the unstable system 74areas (GIS), near thewhich volcano. was created by the USGS [4] and is based on a semi-empirical model that delimits flood 75 riskLAHAR zones Z by was lahar written (that is, to areas delimit drawn areas to repres of potentialent the laharprobable inundation floods during from a one lahar or event) more in a 76user-specified digital elevation lahar volumes. model (DEM). LAHAR Z is a code that is executed within a geographic information 77system (GIS),The whichprogram was uses created two by semi-empirical the USGS [4] andequations is based calibrated on a semi-empirical by statistical model analysis that delimitsin the cross 78flood section risk zones of an by area lahar flooded (that is, by areas a lahar drawn (A) toand represent the flooded the probable planimetric floods area during (B) measured a lahar event) in 27 inlahars 79a digitaldeposits elevation of 9 volcanoes model (DEM). in the United States of America, Mexico, Colombia, Canada and Philippines 80 [6]The (Figure program 2). uses two semi-empirical equations calibrated by statistical analysis in the cross 81section of anThe area equations flooded are: by a lahar (A) and the flooded planimetric area (B) measured in 27 lahars deposits of 9 volcanoes in the United States of America, Mexico,/ Colombia, Canada and Philippines [6] 82 = (1) (Figure2). / 83 The equations are: = (2) 2/3 A = a1V (1) 84 Where A is the maximum section area flooded,2/3 B is the total area flooded and V is the volume B = a2V (2) 85 of the lahar, =0.05 and = 200, are constant values.