Lahars Research Articles

Dynamics of rain-triggered lahars and destructive power inferred from seismo-acoustic arrays and time-lapse camera correlation at Volcán de Fuego, Guatemala

AbstractLahars, or volcanic mudflows, are one of the most devastating natural, volcanic hazards. Deadly lahars, such as the one that occurred after the Nevado del Ruiz, Columbia eruption in 1985, in which at least 23,000 people tragically lost their lives, threaten the safety and well-being of humans, the economy, and the infrastructure of many of the communities living in the vicinity of volcanoes. Due to their complex flow behaviors, lahars remain a major challenge to those studying them. We present an analysis of several rain-triggered lahar events at Volcán Fuego in Guatemala using both seismic and infrasound monitoring to quantify both ground vibrations and low-frequency atmospheric sound waves associated with these mudflows. Geophysical data collected over this field campaign quantifies flow parameters such as velocities, stage and the frequency of these rain-triggered lahars. Time-lapse imagery of lahar flows is compared with filtered seismo-acoustic signal characteristics to ascertain stage predictions and relationship to stage fluxes. Using random forest regression models, we establish moderate correlations (correlation coefficient modes 0.48–0.53) with statistical significance (p value = 0.01–0.02) between signal energetics and respective stage. Compiling a catalog of rain-triggered lahar events in Volcán de Fuego’s drainages over a season permits a dataset amenable to statistical analysis. Our goal is the development of new-generation geophysical monitoring tools that will be capable of remote and real-time estimation of flow parameters.

Effects of root-colonizing fungi on pioneer Pinus thunbergii seedlings in primary successional volcanic mudflow on Kuchinoerabu Island, Japan.

Root-colonizing fungi, such as mycorrhizal fungi and dark septate endophyte fungi, are often found on pioneer plant species during early primary succession. However, little is known about which fungal species are responsible for the establishment of pioneer plants when these symbionts colonize simultaneously. We investigated the root-colonizing fungal communities of Pinus thunbergii that established prior to lichens, bryophytes, and short-lived herbaceous plants in a primary successional volcanic mudflow site on Kuchinoerabu Island, Japan. We collected a total of 54 current-year and 1- to 2-year-old seedlings. The colonization of root fungi was evaluated by direct observation of key structures (e.g., mantle, arbuscule, microsclerotia, and hyphae) and molecular analysis. Of the 34 current-year seedlings collected, only 12 individuals were colonized by ectomycorrhizal (ECM) fungi. By contrast, all 1- to 2-year-old seedlings were colonized by ECM fungi. Seedlings colonized by pine-specific ECM fungi, specifically Rhizopogon roseolus and Suillus granulatus, showed higher nitrogen and phosphorus contents in their needles compared to non-ECM seedlings. Arbuscular mycorrhizal fungi and dark septate endophyte fungi were found in only two and three individuals, respectively. The high density of mycophagous deer on Kuchinoerabu-jima may contribute to the favored dispersal of ECM fungi over other root-colonizing fungi. In conclusion, the seedling establishment of P. thunbergii at the volcanic mudflow may be largely supported by ECM fungi, with negligible effects of arbuscular mycorrhizal fungi and dark septate endophytes.

Uncertainty in measuring the role of climate change on debris-flow triggering on volcanoes - bulk-density, temperature and moisture analysis at Unzen Volcano (Japan)

As climate change creeps into the 21st century, the intensity of debris flows due to heavy and concentrated rainfall has increased in mountainous regions of Japan and East Asia. However, the relationship between climate change and an increase in debris flows is likely to be non-linear. Rainwater infiltrates more quickly into porous material, and the lack of vegetation cover increases evaporation and the temperature of surface sediments. In addition, periodic gully collapses bring fresh layers of porous material that increase the distance between the surface and the vadose zone. Therefore, to understand the relationship between volcanic debris flows (or lahars), parameters such as density, porosity, temperature, and moisture retention must be captured in detail in both time and space. The aim of this paper is to assess the role of loose, coarse, and porous sediments in lahar triggering. The present study was conducted at Unzen volcano in the Tansandani Guly between 31 May and 1 June 2023, 30 years after the last eruption. The dacite material is composed of a matrix of sand and coarse sand mixed with larger fractions and blocks, therefore traditional density measurement methods could not be applied, and a photogrammetric based method was used. In the field, sets of SfM-MVS photographs were taken before and after digging a hole in the sediments so that the measured mass could be compared to the volume of the hole in the sediments. After the sediments were dried, the dry and wet density, bulk density and porosity of the sample were calculated. When compared to the temperature data collected in the field, the following results were obtained: (1) The porosity of the volcanic material was highest in the lower reaches, followed by the upper reaches, and lowest in the middle reaches. This may be because fine sand washed out of the upstream area by rainfall is currently stored in the midstream area, which may facilitate debris flow generation. In addition, the downstream area has a high porosity, which may be due to the surrounding vegetation preventing the influx of new fine sand from the channel wall. (2) Because of the higher porosity and the lack of organic matter and vegetation cover, the increase in temperature acts more directly on the decrease in water content than in mountainous areas. Consequently, empirical equations for the potential for mudslides in volcanic areas with respect to surface temperature and soil moisture need to be developed for hazard and disaster risk management purposes.

Factors controlling volcanic debris flows two decades after the 1990–1995 eruption at Mount Unzen in Japan

Rainfall-triggered volcanic debris flows (VDFs), or lahars, frequently occur during and/or immediately after eruptions, often because of decreases in the infiltration capacity resulting from the deposition of fine volcanic materials. Although the infiltration capacity recovers and the frequency of VDFs decreases within a decade, VDFs have continued to occur over several decades after the eruption of some volcanoes. No study has yet identified the factors controlling sediment discharge of VDFs for a specific volcano after the recovery of infiltration capacity to the pre-eruptive level. We analyzed topographic changes and sediment volumes between 2003 and 2020, using 16 digital elevation models (DEMs) and orthophotographs from aerial lidar scanning for the Tansandani and Gokurakudani gullies of Mount Unzen where the infiltration capacity has recovered after the most recent eruption in 1990–1995. We also analyzed the frequency and magnitude of VDFs in 2003–2020. Topographic changes differed before and after three large-scale VDFs in 2015 and 2016. The total volume of the three VDFs was 140 × 103 m3. Between 2003 and 2014, the width and depth of the gullies continuously increased, with the changes in the intervals of successive DEMs averaging below 5 m. Between 2017 and 2020, gully cross-sections remained U-shaped and changed little, while the channel gradient gradually decreased. U-shaped gullies promote the dispersion of VDFs and their gentle slopes reduce the velocity of VDFs. As a result, the frequency and magnitude of VDFs decreased, and deposition and erosion in the gullies were almost balanced between 2017 and 2020. Thus, we conclude that topography is the main factor that controls the occurrence and magnitude of debris flows and therefore sediment discharge after the recovery of infiltration capacity to the pre-eruptive level.

INVESTIGATIONS ON INSAR DATA PROCESSING STANDARD FOR VOLCANO ISLAND MONITORING IN INDONESIA

Abstract. In critical situations such as disaster and humanitarian relief, the reliable geospatial data will present an appropriate decision on a timely manner. As fundamental datasets, large-scale topographic maps are are mandatory in order to perform geospatial analysis for many societal challenges. Indeed, Large Scale Topographic Mapping in Indonesia shall be accelerated in an innovative and productive way to consider the production efficiency, especially for the geospatial data acquisition as its primary source. Interferometric Synthetic Aperture Radar (InSAR) data acquisition presents some advantages, especially in conjunction with the security clearance and global weather as some main constraints for the geospatial data acquisition. In terms of disaster preparedness and emergency response, radar interferometry techniques can play an important role by generating a Digital Elevation Model (DEM) as an input to Decision Support Systems (DSS). In addition, the techniques of differential Interferometric Synthetic Aperture Radar (D-InSAR) can provide the earth surface deformation from time series Radar Datasets. A set of standards related to the InSAR data acquisition are essential, especially with regards to the improved sensors, and processing methods implemented by the worldwide space agencies nowadays. Hence, the precise definition of a standard is fundamental in order to prepare the InSAR data as one potential source of geospatial data and information, especially for LSTM data production. Generated time series of Digital Elevation Model (DEM) can identify the potential cause of 2018’s Sunda Strait tsunami (Tampubolon, 2019). It was related with the increasing eruption activity of Anak Krakatau (Child of Krakatoa). From DEM analysis, the Volcanic mudflow material avalanche has been detected before the tsunami hit the coastal surrounding area. In this paper, more advanced techniques was investigated by the combination between Time Series DEM Analysis and Ground Displacement detection. The focus on the integration between reliable TanDEM-X and up-to-date Sentinel 1A/B was proposed on another volcano island of Gamalama in Ternate. As TanDEM-X uses X-band as its medium wave, it can produce more reliable DEM as a reference data. On the other hand, Sentinel 1 uses C-band that can contribute to detect the ground deformation over the aforementioned volcano island. TanDEM-X uses a more robust and consistent approach to scan the earth surface by single data acquisition scheme, which is generally more accurate and reliable for the DEM generation. However, many factors influence the selection of a platform that can be best suited for radar interferometry. Initially, the German TanDEM-X Coregistered Singlelook Slant-range Complex (CoSSC) using bi-static InSAR approach has been implemented in order to generate DEMs comply with the LSTM specification in Indonesia. The basic principle is performing a simultaneous measurement of the same scene and identical doppler spectrum by using 2 sensors, thereby avoiding temporal decorrelation (DLR, 2012). Subsequently, the differential InSAR techniques by using Sentinel 1A/B has been performed in order to detect the ground deformation. Finally, tt can be shown that the reliable TanDEM-X data has increased the ground deformation resolution and accuracy in order to provide potential solution for disaster preparedness.

Mapping of Mount Semeru Volcanic Mudflow Susceptibility Along the Rejali River using the GIS-based AHP-TOPSIS Ensemble Approach

Volcanic mudflow floods occur when rainfall runoff combines with volcanic material and flows downstream. These devastating events cause significant damage to infrastructure, disrupt economies, and result in injuries and casualties. One area where the flow of volcanic material greatly affects the situation is the Rejali River, which receives a substantial amount of volcanic debris from Mount Semeru. To address this issue and begin mitigating the associated risks, it is crucial to start by mapping the potential distribution of volcanic mudflow floods. Therefore, this study aimed to assess factors impacting volcanic mudflow flood susceptibility and to create a corresponding susceptibility map. The study employed the Analytical Hierarchy Process (AHP) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) to determine the influence of various factors and classify the areas, respectively. These methods were integrated with the Geographic Information System (GIS) to enhance the analysis. The weighted analysis results showed that the most impactful factors conditioning volcanic mudflow floods, in descending order, were rainfall (42.40%), land cover (13.89%), elevation (13.39%), slope (12.51%), distance from the river (7.09%), soil type (6.58%), and rock distribution (4.13%). The TOPSIS calculation further highlighted that rainfall intensity between 104.03 and 109.65 mm day-1 had the greatest influence on susceptibility. The successful integration of AHP and TOPSIS methods with GIS helped develop a volcanic mudflow flood susceptibility model with an outstanding accuracy of 0.969. The model showed that approximately 46.40% of the areas along the Rejali River exhibited very high susceptibility to volcanic mudflow floods, while an additional 16.21% indicated high susceptibility and substantial risk in most regions. Therefore, the generated susceptibility map offered important insights for shaping future mitigation strategies and influencing policy decisions.

An extraordinary fossil captures the struggle for existence during the Mesozoic

Dinosaurs and mammals have coexisted for the last ~ 230 million years. Both groups arose during the Late Triassic and diversified throughout the Mesozoic and into the Cenozoic (the latter in the form of birds). Although they undoubtedly interacted in many ways, direct fossil evidence for their interaction is rare. Here we report a new fossil find from the Lujiatun Member of the Lower Cretaceous Yixian Formation of China, showing a gobiconodontid mammal and psittacosaurid dinosaur locked in mortal combat. We entertain various hypothesized explanations for this association, but the balance of the evidence suggests that it represents a predation attempt on the part of the smaller mammal, suddenly interrupted by, and preserved within, a lahar-type volcanic debris flow. Mesozoic mammals are usually depicted as having lived in the shadows of their larger dinosaurian contemporaries, but this new fossil convincingly demonstrates that mammals could pose a threat even to near fully-grown dinosaurs. The Yixian Formation—and the Chinese fossil Jehol Biota more broadly—have played a particularly important role in revealing the diversity of small-bodied dinosaurs and other fauna. We anticipate that the volcanically derived obrution deposits specific to the Lujiatun Member will likewise continue to yield evidence for biotic interactions otherwise unknown from the rest of the fossil record.

Quantitative impact assessment of the 2019 tropical cyclone Kammuri lahars: Mayon volcano, Philippines

Lahars (volcanic mudflows) are frequent occurrences in communities near active Philippine volcanoes due to intense and prolonged rainfall. Mayon Volcano is the most active volcano in the Philippines, ejecting pyroclastic deposits that serve as erodible materials for lahars. Damaging lahars have occurred in the past, with the more recent ones in 2006, 2015, 2019 and 2020 posing impacts such as erosion, burial, and flash flooding in low-lying areas. This paper presents the results of an interdisciplinary case study on lahar impact assessment for a selected pilot community at Mayon Volcano. Lahar hazard modeling, an exposure database, and a Filipinized lahar damage state table were combined to estimate potential lahar impacts to buildings for the study area using a lahar impact assessment software tool called REDAS Quick Lahar Impact Simulation Tool (REDAS-QLIST). The tool can estimate lahar losses such as physical damage, economic loss, and total population affected including age-sex distribution. Being able to accurately quantify impact and damage is one of the added values provided by REDAS-QLIST. The damage and loss estimates produced for our case study area were tested using an actual lahar event scenario from Tropical Cyclone (TC) Kammuri in 2019. Stakeholders, especially from local government units, can utilize the methods and results presented to plan and apply adaptable and sustainable disaster risk reduction programs in their communities. Importantly, the methodology can be used with additional lahar modeling results and exposure data through the REDAS QLIST to assess hazard and loss for other volcanic regions in the Philippines.

Infrasound detection of approaching lahars

Infrasound may be used to detect the approach of hazardous volcanic mudflows, known as lahars, tens of minutes before their flow fronts arrive. We have analyzed signals from more than 20 secondary lahars caused by precipitation events at Fuego Volcano during Guatemala’s rainy season in May through October of 2022. We are able to quantify the capabilities of infrasound monitoring through comparison with seismic data, time lapse camera imagery, and high-resolution video of a well-recorded event on August 17. We determine that infrasound sensors, deployed adjacent to the lahar path and in small-aperture (10 s of meters) arrays, are particularly sensitive to remote detection of lahars, including small-sized events, at distances of at least 5 km. At Fuego Volcano these detections could be used to provide timely alerts of up to 30 min before lahars arrive at a downstream monitoring site, such as in the frequently impacted Ceniza drainage. We propose that continuous infrasound monitoring, from locations adjacent to a drainage, may complement seismic monitoring and serve as a valuable tool to help identify approaching hazards. On the other hand, infrasound arrays located a kilometer or more from the lahar path can be effectively used to track a lahar’s progression.

SURFACE FLOWS SIMULATION BY CELLULAR AUTOMATA: A SHORT REVIEW OF THE LLUNPIY MODEL

Lahars represent one of the most destructive natural disasters regarding the loss of human lives, but also for making havoc on public infrastructures and ecological habitats. They are very complex surface flows subdivided into two main categories, primary and secondary lahars. Primary lahars are those that originated directly from eruptive volcanic activity, as in the tremendous 1985 Colombian event of Nevado del Ruiz. In contrast, secondary lahars may occur in post-eruptive events or quiescent periods. This volcanic debris flow, a mixture of water and pyroclastic sediments with high density and viscosity, under steep-slope conditions, is capable of reaching high speeds and can travel great distances. A variety of approaches have been adopted to model the behavior of lahar and to predict the hazards posed to downstream communities: empirical models developed, accounting mainly for some macro-observable phenomena, simple rheological and hydrological models that assume reasonable simplifications as a composition-independent flow behavior or a Newtonian flow regime, partial differential equations (PDE) which approximately describe the lahars, highly complex physics and hydrodynamics, and the Cellular Automata alternative methodology. Cellular Automata are a parallel computational paradigm for modeling complex systems by defining simple laws at a local level that generate a global complex evolution. The research, reported in this book, adopts a Multicomponent (or Macroscopic) Cellular Automata (MCA) approach that was developed for numerical simulation purposes by an interdisciplinary research group in Italy. Its reliability and validation on various past events, related to both primary and secondary lahars and debris flow catastrophic events, produced many significant scientific results.

Discrete modelling of debris flows for evaluating impacts on structures

Lahars (volcanic debris flows) are natural phenomena that can generate severe damage and wreak havoc in densely populated urban areas. The evaluation of the forces and pressures generated by these mass flows on constructions (e.g., buildings, bridges and other infrastructure) is crucial for civil protection, assessment of physical vulnerability and risk management. The current tools developed to model the spread of flows at large scale in densely populated urban areas remain inaccurate in the evaluation of mechanical efforts. Here, we developed a discrete numerical model for evaluating debris-flow (DF) impact forces at the local scale of one structure (pillar or column) like a building, a bridge and other infrastructure. In this model, the large-sized solid particles that damage infrastructures and edifices are explicitly modelled using Distinct Element Method (DEM). We considered the fluid and fine-grained solid particles not only in the frame of the pressure exerted on structures, but also through their effects on the movement of particles, i.e. buoyancy and drag. The fluid velocity field and the fluid free surface obtained from Computational Fluid Dynamics (CFD) calculation based on Navier–Stokes equations are imported in the DEM simulation. This model is able to reproduce a range of magnitudes of DFs in terms of volumes, velocities and flow heights. Finally, the model provides insights on impact forces generated by particles on structures and on hydrostatic and/or dynamic pressure due to the combined effect of fluid and solid phases. The model provides results consistent with existing empirical models.

Perbaikan Tanah Lunak Kombinasi Preloading dengan Prefabricated Vertical Drain Studi Kasus Rencana Tanggul Lapindo Porong

Sidoarjo mud is a volcanic mudflow disaster which until now still emits massive mud, therefore the PPLS plans to increase the construction of the embankment on the east side of the main embankment area to increase the strength of the embankment so that it can anticipate if one day there is an overflow so it does not penetrate the area. other. In the previous soil investigation stage, it was shown that the embankment area had subgrade with a relatively small N-SPT value with a thick soft soil layer up to a depth of 30 meters. The construction of this embankment is planned to be built on subgrade conditions which are classified as soft soil so that in the process before the construction of the embankment is very necessary with the improvement of the subgrade.The method of improving soft soil with thickness is proposed using a combination of preloading with PVD to accelerate settlement.To obtain a design height of 5.50 m, the required initial embankment height is 6.77 m with a compression of 1.307 m. The preloading system without the combination of PVD the time a consolidation degree of 90% (U = 90%) for 82.34 years. While the combination preloading system with PVD size 10 x 0.5 cm with a rectangular installation pattern and installation distance (S) 0.80 m, the time consolidation degree 90% (U = 90%) for 3 weeks. Implementation of gradual hoarding at a rate of 0.5 / week for 14 weeks

Analysis of Local Spatial Data Infrastructure to Support Volcanic Mudflow Mitigation along Putih River, Magelang Regency, Central Java Province, Indonesia

One of the most devastating disasters in Indonesia was the Mount Merapi eruption in 2010. After the eruption there still exists the secondary hazard of volcanic mudflow, which has caused damage and casualties. Volcanic mudflow is a mixture of pyroclastic material and rainwater, meaning that in the rainy season the area along rivers becomes a high volcanic mudflow hazard, including the area along Putih River in Magelang Regency, Central Java Province. The development of Spatial Data Infrastructure (SDI) plays an important role in disaster management, especially in disaster mitigation efforts. Building an SDI which shares information on spatial conditions in the area along the Putih River could save many lives and reduce the risk from volcanic mudflow. This research was conducted employing interview surveys, field surveys and secondary data collection at government institutions. The results of the analysis have provided a geoportal prototype as an information gateway for the mitigation of volcanic mudflow along the Putih River and the reduction of disaster risk both for the government and community.

Case study and event analysis for mitigation of unpredictable volcanic hazard

Volcanology is an extremely important scientific discipline. Shedding light on how and why volcanoes erupt, how eruptions can be predicted and their impact on humans and the environment is crucial to public safety, economies and businesses. Understanding volcanoes means eruptions can be anticipated and at-risk communities can be forewarned, enabling them to implement mitigation measures. Professor Tsukasa Ohba is a scientist based at the Graduate School of International Resource Studies, Akita University, Japan, and specialises in volcanology and petrology. Ohba and his team are focusing on volcanic phenomena including: phreatic eruptions (a steam-driven eruption driven by the heat from magma interacting with water); lahar (volcanic mudflow); and monogenetic basalt eruptions (which consist of a group of small monogenetic volcanoes, each of which erupts only once). The researchers are working to understand the mechanisms of these phenomena using Petrology. Petrology is one of the traditional methods in volcanology but has not been applied to disastrous eruptions before. The teams research will contribute to volcanic hazard mitigation.

A Modeling Approach for Lahar Hazard Assessment: the Case of Tamasagra Sector in the City of Pasto, Colombia

The computational program Titan2F, a two phase flow modeling program, is used to model several hypothetical scenarios of volcanic origin mud flows (lahars) in order to estimate the spacial and temporary evolution of this potentially destructive natural phenomena at its entrance of the city of Pasto, Colombia through the Mijitayo river basin. The predictions of the program suggest that extremely high and destructive dynamic pressures at the entrance to the city can be expected. In addition, our simulations show that half of the Tamasagra and El Bosque neighbors can be inundated with lahar depths of about 1 meter thickness. The program shows to be capable to deal with the modeling of the effect of the streets and buildings on the flow behavior, showing how the streets channelizes the flow governing the path of it. In addition, our results allow to identify regions where the flow loss most of its energy, where mitigation of risk can be suggested.

Predictions of snowmelt type volcanic mudflow under various snow conditions

Predictions of snowmelt type volcanic mudflow under various snow conditions

Enhancing the Strength of Volcanic Mud-based Class C Fly Ash Geopolymer Specimen by Limestone Inclusion

Volcanic mudflow disaster has brought negative impacts in the area around the mudflow. The contents of mud are predominantly silicate and aluminate, which are the primary constituent materials of fly ash-based geopolymer specimen. However, the main issue of fly ash-based geopolymer is the requirement of heat curing due to the low calcium in fly ash precursor. The aim of this research is to identify the effect of limestone inclusion on strength properties of volcanic mud-based class C fly ash geopolymer mortar. The volcanic mud was obtained from Sidoarjo mud in East Java Indonesia. The alkaline activator solution was prepared by mixing 10 Molar sodium hydroxide with sodium silicate with the ratio of 0.67. The compressive strength test was carried out at the age of 28 days. The specimens were cured at room temperature. The results show that the addition of 30% limestone in volcanic mud-based class C fly ash geopolymer specimen gives the highest strength at 28 days. It also improves the setting time rate due to the calcium addition. However, further addition of limestone tends to reduce the strength. This might attribute to the decrease of silicate and aluminate contents in geopolymer specimen along with the limestone addition.

Transmigrasi dan Pembangunan di Indonesia

Abstract Undang-Undang No. 15 tahun1997 concerning transmigration aims to improve the welfare of transmigrants and the surrounding community, as well as improve and make equitable development in the regions and also strengthen the unity and unity of the nation. Transmigration as a government program is very wise in overcoming population problems. Judging from the agrarian politics the transmigration program is still far from a sense of justice where 2% of Indonesia's population controls more than 90% of the territory of the Republic of Indonesia. This transmigration program is a program carried out by the government since the old order and the new order, but the process of land ownership is still not finished. Many migrants who do not yet have certificates on land that should be theirs are marked with certificates. There are still around 2 million hectares of transmigration lahars that have not been certified by the national land agency. Agrarian reform is basically a state program that is run with certain objectives, both economic (social) goals and other political and social goals. The main argument of the implementation of agrarian reform is injustice: inequality in land tenure that gives birth to poverty and leads to social injustice. Key word : transmigration and development Abstrak Undang-Undang Nomor. 15 tahun 1997 tentang ketransmigrasian bertujuan untuk meningkatkan kesejahteraan transmigran dan masyarakat sekitarnya, serta meningkatan dan melakukan pemerataan pembangunan di daerah dan juga memperkukuh persatuan dan kesatuan bangsa. Transmigrasi sebagai program pemerintah yang sangat bijak dalam mengatasi masalah kependudukan. Menilik dari politik agraria program transmigrasi masih jauh dari rasa keadilan dimana 2% dari penduduk Indonesia menguasai lebih dari 90% luas lahan wilayah Republik Indonesia. Program transmigrasi ini sebagai program yang dilakukan pemerintah sejak orde lama dan orde baru, namun proses kepemilikan lahan masih belum selesai. Banyak tansmigran yang belum memiliki sertifikat atas lahan yang seharusnya menjadi milik mereka dengan ditandai adanya setifikat. Masih ada sekitar 2 juta hektar lahar transmigrasi yang belum tersetifikat oleh badan pertanahan nasional. Reforma agraria pada dasarnya adalah program negara yang dijalankan dengan tujuan-tujuan tertentu, baik tujuan (pembangunan) ekonomi maupun tujuan politik dan sosial lainnya. Argumen pokok dari pelaksanaan reforma agraria adalah ketidakadilan: ketimpangan dalam penguasaan tanah yang melahirkan kemiskinan dan berujung pada ketitakadilan sosial. Kata Kunci : transmigrasi dan pembangunan

Thermal history of volcanic debris flow deposits on the eastern flanks of Mt. Taranaki, New Zealand: Implications for future hazards

We use palaeomagnetic methods to decipher the thermal histories of a succession of massive to weakly stratified debris flow deposits (Ngatoro and Te Popo formations) of late Holocene age located on the eastern lower flanks of Mt. Taranaki/Egmont Volcano, western North Island, New Zealand. Results from two sites, Vickers Quarry and Surrey Road Quarry, both c. 9.6 km from the present-day summit, enable us to distinguish between clast incorporation temperatures of about 400 °C and emplacement temperatures between 150 and 200 °C, consistent with observation of superficial charring and desiccation of outer podocarp-hardwood tree trunks at Vickers Quarry. Analysis of palaeomagnetic directions and lithofacies architecture suggest that these deposits were likely initiated as a closely-spaced succession of block-and-ash flows (BAFs) that rapidly cooled as they descended the volcano flanks. Radiocarbon chronology and the widespread occurrence of a palaeosol between the products of the preceding Inglewood eruptive phase, c. 3.4 cal. ka B.P., and the overlying Ngatoro Formation suggest that these two events are temporally unrelated. Certainly, there is no field evidence of contemporaneous explosive volcanic activity that might be related to the emplacement of Ngatoro Formation. However, we suggest that these low-temperature deposits might either relate to collapse of a small emergent lava dome or a cooling dome remnant, possibly emplaced in the aftermath of the Inglewood eruption. How collapse was initiated remains uncertain: the remnant dome may have been rendered unstable by volcano-tectonic or tectonic seismic events and/or by adverse meteorological events. Nevertheless, this study demonstrates that edifice collapse events generating potentially hazardous debris flows can occur independent of specific eruptive activity.

ЦЕПОЧКИ КАТАСТРОФИЧЕСКИХ ГЕОМОРФОЛОГИЧЕСКИХ ПРОЦЕССОВ В РЕЧНЫХ ДОЛИНАХ ВУЛКАНИЧЕСКИХ РЕГИОНОВ, "Геоморфология"

В долинах рек вулканических регионов помимо экзогенных причин катализатором катастрофических процессов являются эндогенные факторы - в первую очередь, извержения, которые часто вызывают сходы вулканических селей - лахаров, обусловленных таянием покрывающих вулканы ледников, снега или выпадением ливневых осадков непосредственно после извержения. Эта последовательность катастрофических событий “извержение - сход вулканического селя” достаточно распространена и хорошо изучена, но при детальном рассмотрении очевидно, что образование грязекаменных потоков в долинах вулканически активных регионов обусловлено весьма разнообразными причинами и в этой цепочке может быть задействовано еще много факторов и агентов. Часто извержение провоцирует серию из 2-3 взаимосвязанных и последовательно развивающихся катастроф, т.е. формируется каскад катастрофических процессов. Опираясь на конкретные примеры, выделены и рассмотрены 15 цепочек катастрофических процессов в долинах вулканических регионов, обусловленных разноплановой вулканической деятельностью и сопутствующими событиями - сейсмическими толчками, изменением топографии местности, гидротермальной активностью, эрозией. Завершающими звеньями цепочек, как правило, являются сходы селей, причем иногда неоднократные. Их формирование обусловлено размывом водотоками поступившего в долины рыхлого материала или же прорывами плотин возникших подпрудных озер. Время реализации всех событий подобной цепочки может превышать несколько десятилетий и даже столетий.