A. M. F. Lagmay

Hummocks: how they form and how they evolve in rockslide-debris avalanches

Hummocks are topographic features of large landslides and rockslide-debris avalanches common in volcanic settings. We use scaled analog models to study hummock formation and explore their importance in understanding landslide kinematics and dynamics. The models are designed to replicate large-scale volcanic collapses but are relevant also to non-volcanic settings. We characterize hummocks in terms of their evolution, spatial distribution, and internal structure from slide initiation to final arrest. Hummocks initially form by extensional faulting as a landslide begins to move. During motion, individual large blocks develop and spread, creating an initial distribution, with small hummocks at the landslide front and larger ones at the back. As the mass spreads, hummocks can get wider but may decrease in height, break up, or merge to form bigger and long anticlinal hummocks when confined. Hummock size depends on their position in the initial mass, modified by subsequent breakup or coalescence. A hummock has normal faults that flatten into low-angle detachments and merge with a basal shear zone. In areas of transverse movement within a landslide, elongate hummocks develop between strike–slip flower structures. All the model structures are consistent with field observations and suggest a general brittle-slide emplacement for most landslide avalanches. Absence of hummocks and fault-like features in the deposit may imply a more fluidal flow of emplacement or very low cohesion of lithologies. Hummocks can be used as kinematic indicators to indicate landslide evolution and reconstruct initial failures and provide a framework with which to study emplacement dynamics.

Deformed symmetrical volcanoes

Analog modeling of volcanic cones traversed by strike-slip faulting was conducted, and the cones were analyzed for deformation characteristics. The study shows that symmetrical volcanoes that have undergone basal strike-slip offset may be deformed internally without manifesting any change in their conical shape. Volcanoes deformed by strike-slip faulting may already have well-developed fractures in their interior, yet still appear as a symmetrical cone, exhibiting concentric contours when viewed on a topographic map. Moreover, slight changes in the basal shape of the cone induced by strike-slip movement can be restored by the relatively faster resurfacing and reshaping processes from the deposition of younger eruptive products. These findings pose a subtle but significant point in the assessment of volcanic landslide hazards: not all perfect cones are undisturbed. The detection of concealed deformation is important because fractures induce further instability in volcanoes and act as slip planes during volcano-collapse events. There are many examples of symmetrical volcanoes in nature. The faultless appearance of such perfect cones can be misleading, which requires careful attention in hazards assessment.

Disseminating near-real-time hazards information and flood maps in the Philippines through Web-GIS

The Philippines being a locus of tropical cyclones, tsunamis, earthquakes and volcanic eruptions, is a hotbed of disasters. These natural hazards inflict loss of lives and costly damage to property. Situated in a region where climate and geophysical tempest is common, the Philippines will inevitably suffer from calamities similar to those experienced recently. With continued development and population growth in hazard prone areas, it is expected that damage to infrastructure and human losses would persist and even rise unless appropriate measures are immediately implemented by government. In 2012, the Philippines launched a responsive program for disaster prevention and mitigation called the Nationwide Operational Assessment of Hazards (Project NOAH), specifically for government warning agencies to be able to provide a 6hr lead-time warning to vulnerable communities against impending floods and to use advanced technology to enhance current geo-hazard vulnerability maps. To disseminate such critical information to as wide an audience as possible, a Web-GIS using mashups of freely available source codes and application program interface (APIs) was developed and can be found in the URLs http://noah.dost.gov.ph and http://noah.up.edu.ph/. This Web-GIS tool is now heavily used by local government units in the Philippines in their disaster prevention and mitigation efforts and can be replicated in countries that have a proactive approach to address the impacts of natural hazards but lack sufficient funds.

A structural model guide for geothermal exploration in Ancestral Mount Bao, Leyte, Philippines

Abstract The Tongonan Geothermal Field is the largest producing geothermal field in the Philippines having an installed capacity of 700 MW. It hosts several major power plants that tap geothermal power from the northern flank of the eroded Ancestral Mount Bao (AMB) volcano in Leyte Island, Philippines. A structural model guide is presented to delineate exploration targets in other flanks of the 1200 km 2 area of the AMB volcano. If applied, the model constrains the coverage of geothermal exploration to areas where more detailed investigations involving geological, geophysical, and geochemical methods can be conducted. Analog sand cone experiments and their comparison with the deformation of the AMB volcano were used to interpret wells within the Tongonan Geothermal Field. The study shows that existing producing wells in Tongonan straddle the crypto-Philippine fault, a N34°W (azimuth=326°) trending master fault inferred to traverse the base of the AMB volcano. This master fault induced fracture-controlled permeability where fluids in the Tongonan Geothermal Field circulate. The structural model suggests that the south-southeastern flank of the AMB directly above the southern extension of the master Philippine fault is an ideal geothermal target amenable to detailed exploration.

Street floods in Metro Manila and possible solutions

Urban floods from thunderstorms cause severe problems in Metro Manila due to road traffic. Using Light Detection and Ranging (LiDAR)-derived topography, flood simulations and anecdotal reports, the root of surface flood problems in Metro Manila is identified. Majority of flood-prone areas are along the intersection of creeks and streets located in topographic lows. When creeks overflow or when rapidly accumulated street flood does not drain fast enough to the nearest stream channel, the intersecting road also gets flooded. Possible solutions include the elevation of roads or construction of well-designed drainage structures leading to the creeks. Proposed solutions to the flood problem of Metro Manila may avoid paralyzing traffic problems due to short-lived rain events, which according to Japan International Cooperation Agency (JICA) cost the Philippine economy 2.4billionpesos/day.

Shallow Landslide Hazard Mapping for Davao Oriental, Philippines, Using a Deterministic GIS Model

Davao Oriental located at 7°30′N and 126°50′E is one of the many landslide-prone provinces in the Philippines experiencing severe rainfall throughout the year. With the increase in population and other infrastructural developments, it is necessary to map the landslide potential of the area, to assure the safety of the people and delineate suitable land for development. In order to produce rainfall-induced shallow landslide hazard maps, Stability Index Mapping (SINMAP) was used over a 5-m interferometric synthetic aperture radar (IFSAR)-derived digital terrain model (DTM). SINMAP is based on the infinite slope stability model. Topographic, soil geotechnical, and hydrologic parameters (cohesion, angle of friction, bulk density, infiltration rate, and hydraulic transmissivity) were assigned to each pixel of the DTM with the total area of 5,164.5 km2 to compute for the corresponding factor of safety. The landslide hazard maps generated using SINMAP are found to be accurate when compared to the landslide inventory from 2003 to 2013. The landslide susceptibility classification was translated to zoning maps indicating areas that are safe from shallow landslides, areas that can be built upon with slope intervention and monitoring, and the no-build areas. These maps complement the structurally controlled landslide, debris flow, and other natural hazard maps that are being prepared to aid proper zoning for residential and infrastructural developments.

Volcanoes magnify Metro Manila's southwest monsoon rains and lethal floods

Many volcanoes worldwide are located near populated cities that experience monsoon seasons, characterised by shifting winds each year. Because of the severity of flood impact to large populations, it is worthy of investigation in the Philippines and elsewhere to better understand the phenomenon for possible hazard mitigating solutions, if any. During the monsoon season, the change in flow direction of winds brings moist warm air to cross the mountains and volcanoes in western Philippines and cause lift into the atmosphere, which normally leads to heavy rains and floods. Heavy southwest monsoon rains from 18-21 August 2013 flooded Metro Manila (population of 12 million) and its suburbs paralyzing the nation’s capital for an entire week. Called the 2013 Habagat event, it was a repeat of the 2012 Habagat or extreme southwest monsoon weather from 6-9 August, which delivered record rains in the mega city. In both the 2012 and 2013 Habagat events, cyclones, the usual suspects for the delivery of heavy rains, were passing northeast of the Philippine archipelago, respectively, and enhanced the southwest monsoon. Analysis of Doppler data, rainfall measurements, and Weather Research and Forecasting (WRF) model simulations show that two large stratovolcanoes, Natib and Mariveles, across from Manila Bay and approximately 70 km west of Metro Manila, played a substantial role in delivering extreme rains and consequent floods to Metro Manila. The study highlights how volcanoes, with their shape and height create an orographic effect and dispersive tail of rain clouds which constitutes a significant flood hazard to large communities like Metro Manila.

Validating the Voice of the Crowd During Disasters

Since the late 1990 s, the intensity of tropical cyclones have increased over time, causing massive flooding and landslides in thePhilippines. Nationwide Operational Assessment of Hazards or Project NOAH was put in place as a responsive program for disaster prevention and mitigation. Part of the solution was to set up nababaha.com(www.nababaha.com) and FloodPatrol which provided the public with a web and mobile phone based application for reporting flood height. This paper addresses the problem of providing an interactive and visual method of validating crowdsourced flood reports for the purpose of helping frontline responders and decision makers in disaster management. The approach involves finding the neighborhood of the crowdsourced flood report and weather station data based on their geospatial proximity and time record. A report is classified as correct if it falls within the obtained confidence interval of the crowdsourced flood report neighborhood. The neighborhood of crowdsourced flood reports are correlated with weather station data, which serves as the ground truth in the validation process. Use cases are presented to provide examples of automatic validation. The results of this study is beneficial to disaster management coordinators, first-line responders, government unit officials and citizens. The system provides an interactive approach in validating reports from the crowd, aside from providing an avenue to report flood events in an area. Overall, this contributes to the study of how crowdsourced reports are verified and validated.

Developing an early warning system for storm surge inundation in the Philippines

A storm surge is the sudden rise of sea water generated by an approaching storm, over and above the astronomical tides. This event imposes a major threat in the Philippine coastal areas, as manifested by Typhoon Haiyan on 08 November 2013 where more than 6,000 people lost their lives. It has become evident that the need to develop an early warning system for storm surges is of utmost importance. To provide forecasts of the possible storm surge heights of an approaching typhoon, the Nationwide Operational Assessment of Hazards under the Department of Science and Technology (DOST-Project NOAH) simulated historical tropical cyclones that entered the Philippine Area of Responsibility. Bathymetric data, storm track, central atmospheric pressure, and maximum wind speed were used as parameters for the Japan Meteorological Agency Storm Surge Model. The researchers calculated the frequency distribution of maximum storm surge heights of all typhoons under a specific Public Storm Warning Signal (PSWS) that passed through a particular coastal area. This determines the storm surge height corresponding to a given probability of occurrence. The storm surge heights from the model were added to the maximum astronomical tide data from WXTide software. The team then created maps of probable area inundation and flood levels of storm surges along coastal areas for a specific PSWS using the results of the frequency distribution. These maps were developed from the time series data of the storm tide at 10-minute intervals of all observation points in the Philippines. This information will be beneficial in developing early warnings systems, static maps, disaster mitigation and preparedness plans, vulnerability assessments, risk-sensitive land use plans, shoreline defense efforts, and coastal protection measures. Moreover, these will support the local government units’ mandate to raise public awareness, disseminate information about storm surge hazards, and implement appropriate countermeasures for a given PSWS.

Effects of basement, structure, and stratigraphic heritages on volcano behavior

Effective natural hazard mitigation requires that the science surrounding geophysical events be thoroughly explored. With millions of people living on the flanks of volcanoes, understanding the parameters that effect volcanic behavior is critically important. In particular, basements can influence the occurrence of volcanic eruptions and landslides. This control by the substrate on volcano behavior usually has been considered questionable or less important than the conditions of the deep magma source. However, due to recent findings, this view is changing, specifically with regard to approaches in assessing volcanic hazards.