Undergraduate Student Thesis
2022
Characterizing the Fluvial Geomorphology and Channel Migration Patterns of the Lower Abra River, Philippines through Remote Sensing and GIS Analyses
Jim Paulo M. Bautista
The Abra River Basin is characterized by a north-south braided stream that merges up to the Tineg River and drains towards the West Philippine Sea (South China Sea) via a west-southwest meandering course passing through Ilocos Sur. Although studies on flooding hazards were conducted in the Abra River Basin, fluvial processes, such as channel migration, are not well constrained. This study assessed the influence of geological, geomorphological, and hydrometeorological factors on the channel migration behavior of the Lower Abra River, particularly its meandering channel. The study focused on the extraction of active channels in the Lower Abra River, measurement of fluvial geomorphological characteristics, calculation of migration rates, and identification of the contributing factors and impacts of channel migration. Topographic maps of the United States Army Map Service (US AMS) and Landsat datasets were used as baseline data for channel positions from 1944 to 2021. Semi-automatic classification in Google Earth Engine (GEE) was performed to extract more recent active channels while manual digitization was executed to delineate the 1944 and 1972 active channels. Channel parameters such as length and width, radius of curvature, and sinuosity were digitally measured in QGIS and ArcGIS to characterize the river bend geometry. The extracted vector lines were compared to map areas of erosion and accretion and estimate migration rates using the digital shoreline analysis system (DSAS) tool. Results showed that the maximum channel length (36.1 km) and sinuosity (1.87) values were recorded during 1944 which decreased to 31.7 km and 1.63, respectively, in the year 1972. Measurements of the channel widths revealed the dominant widening of the channel in the downstream portion of the study area. A total of 7 bends were identified along the stretch of Lower Abra River which include Bends 1 to 3 in the downstream reaches and Bends 4 to 7 in the upstream reaches. The maximum curvature values were documented in Bend 4 while Bends 5 and 6 exhibited moderate curvature changes in the past 80 years. The study also found out that the Lower Abra River is highly accretional with maximum accreted areas recorded from 1944 to 1972. Estimation of migration rate using DSAS presented an average migration distance of 223.79 meters and an average migration rate of 2.94 m/yr. The NRM and EPR values also indicated the intensified migration along Bends 5 and 6. The LRR, on the other hand, yielded an average migration rate of 2.81 m/yr. Correlation with the available data suggests that the high sediment input together with increased precipitation, slope, geomorphological barriers, availability of alluvial plains, and difference in the cohesion of sediments influence the channel migration behavior of the Lower Abra River.
Morphometric Analysis of Taal Volcano in Southern Luzon, Philippines Using High-Resolution Topography Data
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Aldrich Gerard C. Gatbunton
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
The Taal Volcano in Southern Luzon, Philippines is a complex volcano consisting of multiple cinder cones within a caldera and is one of the seven active volcanoes monitored by the Philippine Institute of Volcanology and Seismology (PHIVOLCS). This study describes the geomorphology of the five (5) cones of the Taal Volcano, namely: a) Binintiang Malaki, b) Binintiang Munti; c) Main Crater; d) Mt. Tabaro; and e) Mt. Pira-piraso. Terrain analysis and calculation of the dissection index of the 5 Taal Volcano cones were perfomed by generating slope, aspect, and contour maps, and the calculated dissection index based on the 5-m contour outlines. The results showed that the least dissected is Main Crater with a mean dissection index of 1.21 while the most dissected is Binintiang Munti with a mean dissection index of 1.34 which indicates that a cone’s more eruptive activity results to less dissection. This study will serve as a base study for future morphometric analyses of Taal Volcano.
Morphological Analysis of San Pablo Maars in Laguna using Polymorph-2D
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Ayhin H. Itorma
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
The City of San Pablo in Laguna is characterized by multiple water-filled maars, which were formed from Quaternary volcanism associated with the evolution of the Macolod Corridor. Since maar morphology can often preserve clues on the processes that influenced their formation and evolution, the derivation of significant eruption information from maar crater morphologies is explored. This study utilized the Polymorph-2D plug-in in a geographic information system (GIS) environment to quantify the morphological characteristics of the seven San Pablo maars, namely Sampaloc, Yambo, Pandin, Bunot, Palakpakin, Mohicap, and Kalibato. Results show that the maars are generally circular and equant, with significant variation in crater outlines. Compared to the global maar population (i.e. MaarVLS database), the San Pablo maars are considered average in size and shape. Of the seven water-filled maars analyzed, the Sampaloc Lake was observed to deviate in terms of its crater measurements (i.e. high values of length, width, aspect ratio, and isoperimetric circularity). Applying the calculated morphometric characteristics with the Major-Explosion Dominated (MED) model, eruption characteristics such as explosion energy, tephra volume, and depth were estimated. Tephra volume estimates have a broad range value, with an average volume of 2.36 × 108 m3. The average explosion energy of the maar eruptions was estimated to be 6.41 × 1015 m3. The eruptions responsible for maar formation are hypothesized to occur at a minimum depth of 500m, upon the interaction of shallow sills and water stored in a vesicular rock aquifer. The spatial distribution of maars is attributed to both the local stress regime and the NE-SW trending Mapula dike. Further analysis of geological information is necessary to validate and complement the results of this study.
2023
Shoreline Change Detection and Analysis of the Badoc Coast in Ilocos Norte, Philippines
​
Lhiana Reign S. Bañares
The disaster risk of Philippine coastlines continues to exacerbate because of the influence of intensifying climate-related hazards, such as experiencing the most intense rate of regional sea-level rise (SLR), and escalating vulnerability due to greater demands for utilizing coastal areas in the country; hence, studies to analyze coastal changes are essential for disaster risk reduction and management (DRRM) of coastal hazards such as coastal erosion. This study investigated the shoreline changes and the factors influencing them along the Badoc coast of Ilocos Norte. Differences in the response of rocky and sandy coasts to different geologic, anthropogenic, and meteorologic factors can be evaluated from the bay-headland system of Badoc. The analysis of changes and factors on the Badoc coast was determined by extracting historical shorelines from the satellite imageries available in Planet by PlanetLabs PBC and subjecting them to GIS analysis using the Digital Shoreline Analysis System (DSAS) ArcGIS plug-in by USGS. DSAS casted 50 transects along the ~14 km coastline and computed for statistics, such as rates of shoreline change, and future shoreline forecasts. The results show that the Badoc coast is generally stable to slowly eroding at the rocky morphotypes while intense erosion to low accretion is occurring along the sandy morphotypes for the past nine years. Intense erosion (at -8.23 m/yr) is being experienced at the boundary of Barangays Gabut Sur and Lacuben mainly because of multiple sediment sinks at the foreshore and backshore while low accretion happens at Barangay Saud (at 1.31 m/yr) because of its proximity to sediment sources (e.g., inland dunes). Future shoreline prediction show that most of the Badoc coast will remain stable but dramatic shoreline retreat may occur along Gabut Sur where the current residential areas might be affected by 2043. Information dissemination, community-based objectives assessment, and continuous shoreline monitoring with the aid of higher-resolution satellite imagery are recommended for maintaining and assessing the Badoc coast, particularly along Barangays Gabut Sur and Lacuben where intense erosion rates are ongoing. Based on the characteristics of the Badoc coast and the results of the shoreline assessment conducted in this study, a managed retreat strategy may be the most appropriate disaster risk reduction measure for Badoc communities.
​Coastal Vulnerability Assessment of Reina, Quezon Province Using the Coastal Vulnerability Index (CVI) Method and Geographic Information System (GIS)
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Danise Raine D. Dagatan
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Real, Infanta, and General Nakar (REINA) are coastal municipalities in Quezon Province located on the northeastern coast of Luzon. This region is particularly vulnerable to natural hazards such as storm surges due to its position within the Pacific typhoon belt. Coastal areas such as REINA are also prone to erosion, inundation, and flooding, which are consequences of the rising sea levels associated with climate change. The addition of anthropogenic pressures due to the increasing human settlements along the coast further exacerbates the vulnerability of the region. Therefore, it is crucial to determine the local factors that contribute to this vulnerability and quantify the degree of vulnerability experienced by the coast to develop site-specific adaptation strategies. Hence, the objective of this study is to develop a Coastal Vulnerability Index (CVI) that assesses the relative vulnerability along the 49 km coast of REINA using remote sensing data, historical records, and Geographic Information System (GIS) tools. The CVI in this study incorporates six variables that may contribute to coastal damage resulting from sea level rise (SLR), including regional elevation, coastal slope, shoreline change rate, geomorphology, mean tidal range, and population density. These variables were assigned with vulnerability rankings ranging from 1 to 5, representing very low to very high vulnerability, respectively. The results of the study reveal that 44% of the coast is equally divided into moderate and high vulnerability rankings. Meanwhile 12% was found to be at very high vulnerability, indicating areas that are highly prone to the impacts of SLR. The generated CVI maps for the REINA coast provide decision-makers with comprehensive information for the development of context-based adaptation strategies. Furthermore, the findings of this study serve as a vital foundation for future coastal studies in the REINA region.
Tectonic Implications of Submarine Geomorphological Features in Davao Gulf, Philippines
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Pamela Eyre Victoria R. Lira
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
The seafloor landscape of the Davao Gulf in Mindanao, Philippines has long been established to be influenced by active tectonic processes, but the submarine geomorphology of the area has been sparsely studied despite its geologic setting, tectonic regime, and susceptibility to hazards. This research sought to explore Davao Gulf’s seafloor terrain by identifying its major geomorphic features through a submarine geomorphological map. Land-surface parameters (slope, hillshade, aspect, curvature) were extracted and Red Relief Image Mapping (RRIM) was employed to visualize and highlight areas of interest from the gulf’s offshore bathymetry data. For geomorphometric analyses, Geomorphons automated landform classification via SAGA GIS was used to classify the area into different topographic elements to identify the large-scale landforms. Results revealed a variety of undersea landforms such a ridges, throughs, canyons, gullies, channels, platforms, terraces, and features like mass-wasting scarps and speculated barforms which are attributed to different depositional, erosional, and deformation processes. Additionally, offshore faults and lineaments and faults in the terrain indicate active tectonic processes in the Davao Gulf region. The tectonic and deformation mechanisms present in the Davao Gulf’s seafloor terrain signify the potential risks of offshore tectonic-triggered events such as submarine landslides and tsunamis which are essential for coastal hazard assessment in a vulnerable region like Mindanao.
Analyzing the Viability of a Semi-Automated Terrain Classification Model: A Case Study of the Karst Terrain in Tanay, Rizal
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Reynaldo M. San Jose
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
The Philippines is a country ripe for karst formation, with its high slopes, tropical climate, and the abundance of limestone formation. This is most evident in Tanay, a municipality on the foothills of the Sierra Madre. The highlands of the area boast spectacular karst features of towers, dry valleys, and cave systems. Geomorphological mapping of this area, however, is mostly incomplete. This study assessed the viability of creating a semi-automated model of delineating karst landforms in Tanay, using parameters extracted from digital land surface models (DLSMs). A total of 99 towers and 102 valleys were manually delineated for the study, with 7 parameters (elevation, slope, terrain ruggedness, dissection, openness, circularity, and area) extracted for analysis. Using histogram and normal distribution patterns, the correlation of these parameters with delineated landforms was assessed. Results show that the slope, dissection, openness, and area of towers and valleys composed of limestone-bearing formations fall within identifiable ranges. These parameters are also proportional to the age of the limestone-rich formations, with towers showing a decrease in height, slope, topographic ruggedness, and area with increasing formational age. Valleys, on the other hand, show an increase in values of these parameters, excluding area, with increasing formational age. These findings set the groundwork for a semi-automated terrain classification model by determining the factors relevant to delineation. The creation of a model would expedite mapping, which would ease land-use planning for karst areas, which are vital to groundwater recharge, ecological habitats, and archeological and tourism areas.
2024
Morphological and Sedimentological Analysis of Coastal Boulders in Bolinao, Pangasinan
Marjorie D. Del Mundo
Extreme wave events (EWEs) like storm surges and tsunamis pose threats to coastal areas. Coastal boulder deposits (CBDs) are rocks that are a few meters in scale and serve as geological markers for understanding the past frequencies and magnitude of these events for hazard assessment. This study used recent advancements in the quantification of hydrodynamics such as the velocity equations by Nandasena and others (2022), wave height equations by Benner and others (2010), and photogrammetry, a 3D modeling technique— to infer the transport of five coastal boulders in Bolinao, Pangasinan, Philippines. A field survey revealed porous, rugged, and non-cuboidal carbonate deposits on an intertidal Holocene platform. The Zingg diagram showed one bladed, two prolate, and two equant boulders based on their principal axes. Boulder 2, with the longest a-axis of 10.7 m, has the highest estimated mass value of 577 t. Volume and area estimations showed a decrease from dimension-derived (a-, b-, c-axis) values to model-derived (3D) values. Consequently, calculations adopting the new parameters of Nandasena and others (2022) yielded minimum flow velocity ranges of 4.9 - 9 m/s, 6.1 – 11 m/s, and 10.2 – 18.7 m/s, to transport boulders via sliding, overturning, and saltation, respectively. Comparison with values from their 2011 formulas revealed a general decline. Our findings reveal the influence of boulder morphology (e.g., dimensions) in the overestimation of wave velocity. While current boulder data in Bolinao are insufficient to deduce the transport mechanism by storm or tsunami, inferences can be made by comparing our results with boulders studied in Hernani, Eastern Samar, and Pasuquin, Ilocos Norte. This study further highlights the importance of high-resolution input values in enhancing the calculation and estimation of wave characteristics.
Morphometric Analysis of the QC-Marikina-Montalban Subsegment of the West Valley Fault
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Angelo Luis M. Lintag
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
The West Valley Fault (WVF) is an active dextral strike-slip fault that is part of the Marikina Valley Fault System. The proximity of the WVF to Metro Manila and the surrounding highly populated regions poses hazards in the event of a high-magnitude earthquake event. To examine landscape processes that may provide insight into its tectonic activity, this study applied seven geomorphic indices, namely the basin elongation ratio (Re), hypsometric integral (HI), volume-to-area ratio (RVA), mountain front sinuosity (Smf), valley floor width-to-height ratio (Vf), normalized steepness index (Ksn), and normalized stream length gradient index (SL/k), to the QC-Marikina-Montalban subsegment of the WVF. Values of the geomorphic indices were classified into three classes implying low, moderate, and high relative tectonic activity based on the tectonic implications of the geomorphology. Results from the Re, HI, Smf, and Vf indicated moderate to high relative tectonic activity in the northern to central portions of the subsegment. RVA, Ksn, and SL/k results indicated an almost consistently low relative tectonic activity for the entire subsegment. Indurated lithologies in the northern portion of the subsegment were seen to enhance index values in the area while softer and unconsolidated lithologies in the central and southern portions enhance erosion and dampen index values. Collective interpretation of the indices with the local geology indicated a trend of increasing relative activity in the subsegment from south to north. The study shows morphometric analysis involving geomorphic indices as an effective method for evaluating tectonically active areas with minimal structural data. The highly deformed northern and central portions of the subsegment warrant further studies that may bring additional insights into the seismic hazard potential of the WVF.
Determining the Morphological Characteristics of Alluvial Fans in Tectonically Active and Stable Regions
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Mark Bryan C. Olata
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Alluvial fans are arcuate-shaped depositional environments that have been more thoroughly studied in the arid and semi-arid regions. Meanwhile, alluvial fans in the Philippines, a humid and tectonically dynamic country, have yet to be fully understood. Previous works have indicated that the observations and parametric relationships found in other regions do not necessarily apply to alluvial fans in humid areas, more so in both a humid and tectonically active region. This study aimed to elucidate and compare the geomorphological parameters of alluvial fans between two contrasting terranes in the Philippines: the tectonically active Philippine Mobile Belt (PMB) and the aseismic Palawan Microcontinental Block (PCB). Twelve (12) alluvial fans were mapped in this study using the 5-m resolution interferometric synthetic aperture radar digital elevation models (IfSAR-DEMs): six (6) in Nueva Ecija, a province transected by the Philippine Fault Zone (PFZ) and six (6) in Palawan, a region that rarely experiences earthquakes. Parameters such as slope and area were measured both for the alluvial fans and their respective catchments. Longitudinal and transverse profiles were also created to see the topographic changes in the catchment and alluvial fan surfaces. Results show that alluvial fans in Nueva Ecija have generally smaller areas and steeper slopes than the alluvial fans in Palawan. It was also found that the alluvial fan and catchment area have a strong positive correlation in both regions, which confirms the previous generalizations for alluvial fans on these two parameters. Meanwhile, for the fan area and fan slope, the results in the two regions differ significantly. In Nueva Ecija, there is a high negative correlation which is contrasted by the low negative correlation found in Palawan. The same was observed for the catchment area and fan slope for both regions, where there is a high negative correlation in Nueva Ecija but a low negative correlation in Palawan. With this, recent debris flow episodes and the proximity of Nueva Ecija to the PFZ are theorized to have resulted in the steeper and smaller alluvial fans in Nueva Ecija. In contrast, the formation of larger and less steep alluvial fans in Palawan is attributed to the tectonic stability of Palawan. Assuming all other variables are controlled, it was inferred that the highly active tectonic setting of Nueva Ecija conforms to the prevalent global observations in alluvial fan geomorphology, while the results in Palawan have rather deviated from these current theories.
Characterizing The Fault Kinematics of the Bangui Fault, Apayao Through Morphotectonic Analysis
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Justin M. Sarmiento
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
The geologic and tectonic setting of the Philippines is a product of the plate interactions among the Pacific, Eurasian, and Indo-Australian Plates, resulting in the development of the 1200-km-long strike-slip Philippine Fault. The Bangui Fault, located in Apayao, Northern Luzon, represents the northernmost major strand of the Philippine Fault and is considered active based on offset geomorphic features. The Bangui Fault remains relatively understudied, and this study addresses this research gap by applying quantitative methods to characterize the fault kinematics of the Bangui Fault. Utilizing red relief image maps (RRIM) derived from interferometric synthetic aperture radar (IFSAR) digital elevation models (DEMs), this research aims to delineate and measure horizontal and vertical displacements of offset geomorphic features and estimate relative slip rates along the Bangui Fault. The Bangui Fault was divided into eight (8) sections and piercing points (e.g., offset streams and ridges) were measured at each section. A total of 105 offset geomorphic features were identified, and the vertical and horizontal displacements of each feature were measured. The V/H ratio was used to determine the dominant fault kinematics of the Bangui Fault. Across all geomorphic features, the horizontal component is significantly higher than the vertical component. Offset features affirm that the Bangui Fault is a strike-slip fault, with a sinistral sense of motion. This research not only offers practical applications for disaster risk reduction but also addresses a knowledge gap on the tectonic activity of faults in Northern Luzon. By augmenting methodologies from previous studies, this research aims to provide new baseline data for the Bangui Fault's morphotectonic characteristics, providing valuable insights into its behavior and contributing to our understanding of active fault systems in the region.
2025
Relative Sea-Level Changes and Past Tectonic Events in Paraoir, Balaoan, La Union, Philippines Deduced from Uplifted Coral Reef Terraces
Angelica Joy G. Africa
Investigation of emerged coral reef terraces in northwest Philippines was conducted to discuss past relative sea-level (RSL) changes and the influence of tectonic structures in the forearc region of the Manila Trench. The coastal region of Paraoir, Balaoan, La Union, Philippines, was mapped to delineate the distribution and elevation patterns of marine terraces over a span of 300 m. Real-Time Kinematic Global Navigation Satellite System (RTK-GNSS) surveys and topographic analyses were conducted to describe the morphology of the emerged marine platforms. Results reveal 1 to 2 steps of terrace platforms (namely T1 and T2) that rise from 1.2 to 3 m amsl and platform widths ranging from 6 to ~14 m. Widths and shoreline angles (i.e., inner edge) of T2 were not measured in detail due to limitations in the RTK survey caused by dense vegetation landward of the platform. Coastal notches were also measured, with the height and depth of their apex indicating the modern tidal range. The staircase-like topography of horizontal to sub- horizontal platforms, along with 0.6 to 2 m terrace risers, suggests that these geomorphic features possibly resulted from m-scale coseismic events. Forward elastic dislocation modeling was conducted to constrain fault rupture parameters that could approximate the observed uplift patterns onshore. Preliminary models suggest that an inferred northeast trending, landward-dipping reverse fault, ~36 km west of Paraoir, may be responsible for the uplift. In contrast, modeling a megathrust segment of the Manila Trench would lead to widespread subsidence in the coastal area. This study contributes valuable insights into understanding geological processes in tectonically active regions, such as the northwest Luzon coastal plain, and complements existing studies on vertical surface deformations, enhancing local understanding of risk and hazard assessment.
Beachrock Occurence in Luna, La Union as an Indicator of Relative Sea-Level Change
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Zebedee Trebur M. Aguas
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
​Sea-level rise through the 20th and 21st centuries has been accelerating based on observational data from coasts around the world, threatening coastal communities, especially in the Philippines. Thus, accurate reconstructions of local past relative sea-level (RSL) variations are essential in planning for future coastal developments. Research on beachrocks has demonstrated their potential as sea-level indicators. In this study, lithofacies and petrographic analyses are done on the beachrocks along the coast of Luna Beach in La Union to provide insights into the relative sea-level history in the area. Five distinct lithofacies were identified: (1) massive pebbly sandstone, (2) coral framestone, (3) massive conglomerate with coral cobble, (4) massive coral-rich conglomerate, and (5) tabular cross-stratified pebbly sandstone, indicating a lower foreshore to upper shoreface paleoenvironment. On the other hand, petrographic analysis revealed acicular meniscus cement, micritic envelopes, and pendant cementation, attributed to the foreshore paleoenvironment. Two interpretations of the relative sea-level history in the area after beachrock formation are presented from calculations of the indicative meanings and RSL. The foreshore interpretation from the cement characteristics suggests a RSL fall of 0.04 ± 0.38 m to a RSL rise of 0.24 ± 0.38 m. Meanwhile, the upper shoreface interpretation from lithofacies analysis suggests a maximum RSL rise of 0.047 m to a minimum RSL fall of 0.074 m to 0.741 m. These different paleoenvironmental interpretations from the lithofacies and petrographic analyses highlight the variability of cement and lithofacies characteristics and the need to gather modern analogs in subtidal, intertidal, and supratidal settings.
Karstification Potential Mapping of Dalaguete, Cebu Using GIS and Weight of Evidence Method
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Kryzell M. Carmona
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Karstification refers to the chemical or mechanical processes that dissolve highly soluble rocks, which can be measured through karstification potential mapping. The Philippines hosts extensive tropical karst landscapes, marked by sinkholes, caves, subterranean rivers, and cliffs. Given these, this study assessed the karstification potential of Dalaguete, Cebu by examining the influence of geological and climatic factors using Geographic Information Systems (GIS) and the Weight of Evidence (WoE) method. WoE is a probabilistic model that uses binary maps, treating each factor as evidential input for predicting a phenomenon. Positive weights (W+) indicate a factor’s contribution to the presence of an event, while negative weights (W−) suggest association with the absence. The weight of contrast (C) measures the spatial association between the factor and evidence data, while the final weight (Wf) reflects the overall influence of each class. Preliminary analysis included reconnaissance fieldwork and geomorphological mapping, which identified two types of karst. Old-mature karst is characterized by high relief, steep slopes, cockpit, kegelkarst, and coalesced sinkholes, indicating an advanced stage of karstification. In contrast, mature-young karst features marine terraces, low-lying hills, and sinkholes, suggesting an early stage of karst development. WoE results showed that karstification is most positively influenced by mature limestone (Butong Limestone, Mantalongon Limestone, Barili Formation), moderate lineament density (0.287-0.429 km/km2), low drainage density (1-2 km/km2), sparse vegetation (perennial & annual crops), flat slopes (<6.5°), high elevation (624 – 832 m), very low temperature (<24°C), and high precipitation (175 – 183 mm/month). Conversely, clastics with limestone (Calagasan Formation), very high lineament density (>0.573 km/km2), high drainage density (3-4 km/km2), very dense vegetation (mangrove forest), very steep slopes (>45°), moderate elevation (416-624 m), moderate temperature (25-26°C), and low precipitation (159-167 mm/month) most negatively impact karstification. The resulting karstification potential map effectively identified very high and very low potential zones, validated by the sinkhole inventory and ground-validated points (e.g., caves, sinkholes, and springs), with an Area Under the Receiver Operating Characteristic (AUROC) Curve of 0.680. These findings aim to guide local land-use planning, hazard mitigation, and resource management, while also advancing karst research in Cebu through the application of the WoE method.
Determining the Factors Influencing the Evolution of the Sta. Cruz and Lumban Deltas in Laguna de Bay
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Francheska Venica A. Contreras
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Deltas hold both environmental and economic value, providing ecosystem services and livelihoods for the people. To prevent their decline, it is important to identify factors that influence their evolution. Given this, the study focuses on the Sta. Cruz and Lumban deltas located in the eastern lobe of Laguna de Bay. In this study, the QGIS Shoreline Change Analysis Tool (QSCAT), a Quantum Geographic Information Software (QGIS) plugin, was used to perform shoreline change analysis on the study area, yielding results for Net Shoreline Movement (NSM), Shoreline Change Envelope (SCE), and End-Point Rate (EPR). Since the QSCAT plugin has not been used on deltaic environments before, a second shoreline change analysis was conducted using the Digital Shoreline Analyis System (DSAS) version 6 application to solidify results. The SCE results show the overall spatial change undergone by the study area from 2017-2023, with extensive changes identified to the east of the Sta. Cruz delta and the western side of the Lumban delta. Meanwhile, the NSM and EPR results define the temporal aspect of this change, illustrating that the delta shorelines primarily experienced erosion. Meanwhile, accretionary patterns were identified where delta shorelines were facing against the direction of the lake circulation which flows southwest from the East Bay to the South Bay. In addition, the stable patterns occurred around built-up areas along the coast. The extensive destruction of croplands in the Sta. Cruz Delta were traced to storm and rainfall events in 2022, specifically the passage of tropical cyclones, Karding and Paeng, and the La Niña conditions that lasted until January 2023. This area was found to experience regular flooding, raising concerns on flood mitigation measures to prevent the endangerment of life and loss of livelihoods. The lakeward trend of urbanization was also identified, temporarily increasing the sediment supply but also increasing the shorelines’ vulnerability to erosion. Meanwhile, definitive conclusions could not be made for the Lumban Delta owing to conflicting literature and highly variable areas. Climate change in relation to increasing the variability of storm and rainfall events as well as human activity were identified as the key factors for delta evolution. Confounding factors such as sea level rise and manmade structures are also discussed. Finally, the transect length needed to accommodate shoreline extents caused intersections which complicated the interpretation of numerical values. The implications of these are discussed in relation to the QSCAT instabilities and gaps in existing literature.
Liquefaction Susceptibility Analysis of the Aringay-Agoo-Santo Tomas Coastal Plain
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Tiara U. Liporda
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
To refine the existing liquefaction susceptibility map of the Aringay-Agoo-Santo Tomas coastal plain, this study aimed to determine areas of high, moderate, and low liquefaction susceptibility within the study area by overlaying hydrological, geomorphological, and historical input maps with equal weights using raster overlay in a Geographic Information System (GIS). Input maps were generated from static water level data, manual delineations from satellite images, and available historical liquefaction data and reports. Supplementary maps, such land cover and soil type, provided additional detail. The correlation of the factors with the final map and among each other were assessed using cell statistics (range) by quantifying the cell deviation values. This tool subtracts the minimum value to the maximum value per pixel. Lower cell deviation values, indicating high correlation, was exhibited only by the geomorphic map, confirming its dominant role in determining presence of liquefiable soils. Furthermore, the influence and impact of these factors on the overall liquefaction susceptibility was assessed using a one-at-a-time sensitivity analysis. This investigates the variations of the output map caused by variations in the input parameters to determine which factor has the largest degree of influence. The ranking of the factors, with decreasing influence are: soil type, RWB, GWL, HLO, land cover, and geomorphology. This highlighted the sensitivity of liquefaction susceptibility to factors with implications on soil saturation (i.e., soil type, RWB, GWL), attributed to the direct relationship of hydrological factors to the presence of pore waters. Interestingly, implications on interactions between geomorphology and hydrological factors may be derived from soil type data.
Analysis of Knickpoint Zones in the Abra River Basin, Northern Luzon, Philippines
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Rex Gabriel P. Orbita
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Knickpoints are localized sharp slope changes within a river profile, occurring as a response to tectonic deformation, differential erosion across lithologies, coarse bed load, or base-level changes. As such, knickpoints are then utilized to investigate the response of bedrock fluvial systems in the landscape evolution of the Abra River Basin (ARB). The ARB is 4,887 sq.km. river basin spanning the provinces of Abra, Ilocos Sur, Benguet, and Mountain Province in northwest Luzon. A 5-m resolution IfSAR DEM was used to perform topographic analysis using the TopoToolbox program on MATLAB, in which more than 2,800 knickpoints were extracted. The knickpoints were visually validated using Google Earth Imagery and a Red Relief Image Map, with a final count of over 2,500 knickpoints. Morphological analyses indicate that, on average, knickpoints in the ARB occur within elevations of 830 m, and along slightly convex moderate slopes (22.49° slope, -0.03 openness). A majority of the knickpoints (n= ~800) occur within the Late Cretaceous to Eocene Pugo Formation, followed by the Oligocene Central Cordillera Diorite Complex, while the rest occur in Cenozoic sedimentary and volcaniclastic formations. Kernel Density Estimation (KDE) values show high clustering in the Tineg and Cervantes watersheds. The knickpoints are also found to be near faults like the Abra River Fault, formational contacts, and lineaments. Optimized Hot Spot Analyses indicate that the clustering within faults, lineaments, and contacts may correlate with such structures. Some knickpoint zones overlap within these clusters, suggesting a more complex interaction between geological controls of fluvial landscape evolution.
Slope Stability Assessment of the Abra River Basin, Northern Luzon, Philippines
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Alena W. Taladua
Lyndon P. Nawanao Jr. and Noelynna T. Ramos
Landslides involve a downslope movement of rock or soil along curved (rotational) or planar (translational) rupture surfaces, wherein much of the material often moves as a coherent or semi-coherent mass with little internal deformation (Highland & Bobrowsky, 2008). The Abra River Basin (ARB), characterized by rugged topography and active fault systems, is highly susceptible to geological hazards such as landslides, earthquakes, and urban flooding. This study assesses slope stability in the ARB by analyzing the influence of geomorphological factors on landslide distribution. With a total of 5,411 landslide data points identified and digitized, a Weight of Evidence (WoE) analysis was employed to quantify the spatial associations between landslide occurrence and various geomorphological factors. Results show that slope instability in the area is positively associated with: (1) steep to very steep slopes; (2) convex curvatures; (3) south- to east-facing slopes; (4) moderate drainage density; (5) elevations between 516–1032 m; (6) peaks, spurs, and ridge-related landforms; (7) igneous intrusives, metavolcanics, and clastic sedimentary rocks; (8) grassland and shrubland cover; (9) distances >300 m from roads; and (10) proximity <1500 m to lineaments. The predictive slope stability model achieved an Area Under the Curve (AUC) value of 0.858, indicating very good performance. These findings offer critical insight for landslide susceptibility mapping and risk-informed land use planning in the ARB.