Object-Based Geomorphological Mapping: Application on an Alpine Deep-Seated Gravitational Slope Deformation Contest (Germanasca Valley, Western Alps—Italy)

This research reports the use of a new method of geomorphological mapping in GIS environments, using a full-coverage, object-based method, following the guidelines of the new geomorphological legend proposed by ISPRA–AIGEO–CNG. This methodology is applied to a tributary valley of the Germanasca Valley, shaped into calcschist and greenschist, of the Piedmont Zone (Penninic Domain, Western Alps). The investigated sector is extensively affected by dep-seated gravitational slope deformation (DSGSD) that strongly influences the geological setting and the geomorphological features of the area. The mapping of these gravitational landforms in a traditional way creates some difficulties, essentially connected to the high density of information in the same site and the impossibility of specifying the relationships between different elements. The use of the full-coverage, object-based method instead is advantageous in mapping gravitational evidence. In detail, it allows for the representation of various landforms in the same sector, and their relationships, specifying the size of landforms, and with the possibility of multiscale representation in the GIS environment; and, it can progressively be update with the development of knowledge. This research confirms that the use of the full-coverage, object-based method allows for better mapping of the geomorphological features of DSGSD evidence compared to classical representation.

Karakterisasi Hidrogeologi Daerah Sekitar Tapak PLTN di Bengkayang, Kalimantan Barat

ABSTRAK. Evaluasi tapak merupakan tahap penting dalam penentuan lokasi calon tapak PLTN skala komersial di Indonesia. Aspek–aspek yang dikaji dalam evaluasi tapak berdasarkan peraturan yang berlaku antara lain aspek geoteknik dan aspek dispersi zat radioaktif. Untuk mendukung kajian aspek tersebut maka perlu adanya kajian karakterisasi hidrogeologi daerah sekitar tapak. Tujuan penelitian ini adalah menentukan karakteristik hidrogeologi daerah sekitar tapak PLTN di Kabupaten Bengkayang, Provinsi Kalimantan Barat berdasarkan aspek geologi dan geofisika. Metode yang dilakukan adalah pemetaan geomorfologi, pemetaan geologi, pemetaan hidrogeologi, pengukuran geolistrik, serta analisis terpadu. Secara morfologi, daerah penyelidikan dibagi menjadi tiga satuan, yaitu dataran aluvial, bukit terisolasi, dan dataran pantai. Secara stratigrafi, satuan batuan yang ditemukan berurutan dari tua ke muda adalah andesit, granodiorit, diorit, endapan pasir kuarsa, endapan pantai, dan endapan aluvial. Pengukuran geofisika menggunakan metode geolistrik dilakukan pada 12 lintasan dengan masing-masing panjang lintasan 470 m dan spasi elektroda 10 m. Pada penampang geolistrik ditemukan beberapa anomali pada kompleks batuan beku yang mengalami frakturasi atau tubuh diorit yang menerobos satuan andesit. Nilai anomali ini berkisar antara 300 Ωm dan >8000 Ωm. Nilai resistivitas yang sangat rendah (<30 Ωm) diinterpretasikan sebagai endapan aluvial yang jenuh air dengan ketebalan mencapai ±100 m. Daerah penelitian dapat dibagi menjadi tiga satuan hidrogeologi; akuifer dengan aliran melalui ruang antarbutir kelulusan tinggi, akuifer dengan aliran melalui ruang antarbutir kelulusan sedang, dan akuifug setempat berarti. Secara umum pola aliran tanah bebas mengalir relatif dari SSW ke NNE.ABSTRACT. Site evaluation is an important phase of site selection for commercial-scale nuclear power plants (NPP) in Indonesia. Geotechnical and radioactive material dispersion aspects are some of the aspects which are assessed in site evaluation under provisions of laws and regulations. To support those aspect evaluations, it is necessary to conduct hydrogeological characterization in the vicinity of the NPP site. The purpose of this study is to determine the hydrogeological characteristic of the vicinity of the NPP site in Bengkayang Regency, West Kalimantan Province based on geological and geophysical aspects. The methods of this study consist of geomorphological mapping, geological mapping, hydrogeological mapping, geoelectric measurement, and integrated analysis. The study area consists of three morphological units: alluvial plain, isolated hills, and coastal plain. Stratigraphically, the lithology units of the study area, from the oldest to the youngest, consist of andesite, granodiorite, diorite, quartz sand deposits, coastal deposits, and alluvial deposits. The geophysical measurement used is the geoelectric method which is conducted at 12 electrode arrays with 470 m length and spacing of 10 m. In the geoelectrical section, it can be seen that several anomalies can be interpreted as the fractured body of igneous rocks or the diorite intrusion in andesite. These anomaly values are ranged from 300 Wm to >8000 Wm. The relatively low resistivity values (<30 Wm) are interpreted as water saturated-alluvial deposits that could have a thickness of ±100 m. There are three hydrogeological units in the study area: aquifers in which flow is intergranular with high permeability, aquifers in which flow is intergranular with moderate permeability, and aquifug of local importance. Generally, the groundwater in the study area flows from SSW to NNE.

Northeastern Patagonian Glacier Advances (43°S) Reflect Northward Migration of the Southern Westerlies Towards the End of the Last Glaciation

The last glacial termination was a key event during Earth’s Quaternary history that was associated with rapid, high-magnitude environmental and climatic change. Identifying its trigger mechanisms is critical for understanding Earth’s modern climate system over millennial timescales. It has been proposed that latitudinal shifts of the Southern Hemisphere Westerly Wind belt and the coupled Subtropical Front are important components of the changes leading to global deglaciation, making them essential to investigate and reconstruct empirically. The Patagonian Andes are part of the only continental landmass that fully intersects the Southern Westerly Winds, and thus present an opportunity to study their former latitudinal migrations through time and to constrain southern mid-latitude palaeo-climates. Here we use a combination of geomorphological mapping, terrestrial cosmogenic nuclide exposure dating and glacial numerical modelling to reconstruct the late-Last Glacial Maximum (LGM) behaviour and surface mass balance of two mountain glaciers of northeastern Patagonia (43°S, 71°W), the El Loro and Río Comisario palaeo-glaciers. In both valleys, we find geomorphological evidence of glacier advances that occurred after the retreat of the main ice-sheet outlet glacier from its LGM margins. We date the outermost moraine in the El Loro valley to 18.0 ± 1.15 ka. Moreover, a series of moraine-matching simulations were run for both glaciers using a spatially-distributed ice-flow model coupled with a positive degree-day surface mass balance parameterisation. Following a correction for cumulative local surface uplift resulting from glacial isostatic adjustment since ∼18 ka, which we estimate to be ∼130 m, the glacier model suggests that regional mean annual temperatures were between 1.9 and 2.8°C lower than present at around 18.0 ± 1.15 ka, while precipitation was between ∼50 and ∼380% higher than today. Our findings support the proposed equatorward migration of the precipitation-bearing Southern Westerly Wind belt towards the end of the LGM, between ∼19.5 and ∼18 ka, which caused more humid conditions towards the eastern margins of the northern Patagonian Ice Sheet a few centuries ahead of widespread deglaciation across the cordillera.

Assessing the Prediction Accuracy of Geomorphon-Based Automated Landform Classification: An Example from the Ionian Coastal Belt of Southern Italy

Automatic procedures for landform extraction is a growing research field but extensive quantitative studies of the prediction accuracy of Automatic Landform Classification (ACL) based on a direct comparison with geomorphological maps are rather limited. In this work, we test the accuracy of an algorithm of automatic landform classification on a large sector of the Ionian coast of the southern Italian belt through a quantitative comparison with a detailed geomorphological map. Automatic landform classification was performed by using an algorithm based on the individuation of basic landform classes named geomorphons. Spatial overlay between the main mapped landforms deriving from traditional geomorphological analysis and the automatic landform classification results highlighted a satisfactory percentage of accuracy (higher than 70%) of the geomorphon-based method for the coastal plain area and drainage network. The percentage of accuracy decreased by about 20–30% for marine and fluvial terraces, while the overall accuracy of the ACL map is 69%. Our results suggest that geomorphon-based classification could represent a basic and robust tool to recognize the main geomorphological elements of landscape at a large scale, which can be useful for the advanced steps of geomorphological mapping such as genetic interpretation of landforms and detailed delineation of complex and composite geomorphic elements.

Debris flow event on Osorno volcano, Chile, during summer 2017: new interpretations for chain processes in the southern Andes

Debris flow generation in volcanic zones in the southern Andes has not been widely studied, despite the enormous economic and infrastructure damage that these events can generate. The present work contributes to the understanding of these dynamics based on a study of the 2017 Petrohué debris flow event from two complementary points of view. First, a comprehensive field survey allowed us to determine that a rockfall initiated the debris flow due to an intense rainfall event. The rockfall lithology corresponds to lava blocks and autobrecciated lavas, predominantly over 1500 m a.s.l. Second, the process was numerically modelled and constrained by in situ data collection and geomorphological mapping. The event was studied by back analysis using the height of flow measured on Route CH-255 with errors of 5 %. Debris flow volume has a high sensitivity with the initial water content in the block fall zone, ranging from 4.7×105 up to 5.5×105 m3, depending on the digital elevation model (DEM) used. Therefore, debris flow showed that the zone is controlled by the initial water content available previous to the block fall. Moreover, our field data suggest that future debris flows events can take place, removing material from the volcanic edifice. We conclude that similar events could occur in the future and that it is necessary to increase the mapping of zones with autobrecciated lava close to the volcano summit. The study contributes to the understanding of debris flows in the southern Andes since the Osorno volcano shares similar features with other stratovolcanoes in the region.

GEOMORPHOLOGICAL MAPPING OF THE SERIDÓ REGION, RIO GRANDE DO NORTE STATE/MAPEAMENTO GEOMORFOLÓGICO DA REGIÃO DO SERIDÓ, ESTADO DO RIO GRANDE DO NORTE

O mapeamento geomorfológico do Seridó é necessário devido à escassez de produtos dessa natureza, assim como, também, é importante para fins de planejamento e ordenamento territorial, haja vista que a região analisada apresenta cidades em fase de expansão, como, por exemplo, Caicó e Currais Novos. Este trabalho objetivou realizar um mapeamento geomorfológico da Região do Seridó, Estado do Rio Grande do Norte, até o 4º táxon, na escala de 1:100.000. A base de dados utilizada para o mapeamento foi obtida do SRTM (Shuttle Radar Topographic Mission), com resolução espacial de 30 m, onde foram obtidas curvas de nível, sombreamento do relevo, declividade e hipsometria, além de imagens do satélite LANDSAT 8, para distinção de fisionomias. A partir de então, foi possível distinguir as unidades morfoestruturais e morfoesculturais, além de subunidades morfoesculturais e modelados. Os referidos dados servirão de base para o planejamento e gestão ambiental da área de estudo, uma vez que constituem preciosas informações da geodiversidade regional.

Application of Rock Weathering and Colonization by Biota for the Relative Dating of Moraines from the Arid Part of the Russian Altai Mountains

For the Altai Mountains’ region, especially the arid southeastern part of the Russian Altai, the data on glacier fluctuations in the Pleistocene and Holocene are still inconsistent. The study area was the Kargy River’s valley (2288–2387 m a.s.l.), a location that is not currently affected by glaciation and the glacial history of which is poorly studied. Field observations and geomorphological mapping were used to reveal the configuration of Pleistocene moraines. The relative dating method was applied to define the degree of weathering as an indicator of age. Three moraine groups of different ages (presumably MIS 6, MIS 4, and MIS 2) were identified based on a detailed investigation of their morphological features and the use of relative dating approaches. The latter were primarily based on weathering patterns. Data on the rock mineralogy, porosity, and specificity of biological colonization as an agent of weathering were obtained for the moraine debris. The studied moraines were composed of fine-grained schist, in which the specific surface area and fractality (self-similarity) were more developed in the older moraine. The growth of biota (crustose lichen and micromycetes) colonizing the rock surface led to rock disintegration and the accumulation of autochthonous fragments on the rock surface. Despite the fact that the initial stage(s) of moraine weathering affected by biota was fixed, the correlation trends of biota activity and moraine ages were not determined.

Using data-driven algorithms for semi-automated geomorphological mapping

In this paper, we compare the performance of two data-driven algorithms to deal with an automatic classification problem in geomorphology: Direct Sampling (DS) and Random Forest (RF). The main goal is to provide a semi-automated procedure for the geomorphological mapping of alpine environments, using a manually mapped zone as training dataset and predictor variables to infer the classification of a target zone. The applicability of DS to geomorphological classification was never investigated before. Instead, RF based classification has already been applied in few studies, but only with a limited number of geomorphological classes. The outcomes of both approaches are validated by comparing the eight detected classes with a geomorphological map elaborated on the field and considered as ground truth. Both DS and RF give satisfactory results and provide similar performances in term of accuracy and Cohen’s Kappa values. The map obtained with RF presents a noisier spatial distribution of classes than when using DS, because DS takes into account the spatial dependence of the different classes. Results suggest that DS and RF are both suitable techniques for the semi-automated geomorphological mapping in alpine environments at regional scale, opening the way for further improvements.

GEOMORPHOLOGICAL MAPPING OF THE CHORÓ RIVER HYDROGRAPHIC BASIN - CEARÁ, BRAZIL/MAPEAMENTO GEOMORFOLÓGICO DA BACIA HIDROGRÁFICA DO RIO CHORÓ- CEARÁ, BRASIL

O presente trabalho apresenta o mapeamento geomorfológico da Bacia Hidrográfica do Rio Choró, seguindo os critérios estabelecidos por Ross (1992), com base em condicionantes morfoestruturais e morfoesculturais. A escala de mapeamento (1:75.000) permitiu a delimitação das seguintes unidades: 1º Táxon - Unidades Morfoestruturais - Embasamento Cristalino, Grupo Barreiras, Depósitos Aluviais e Costeiros; 2º Táxon - Unidades Morfoesculturais (Maciços Residuais, Depressão Sertaneja, Tabuleiros, Planícies Fluviais, Lacustres e Litorânea); 3º Táxon - (Depressão Sertaneja Aplainada e Dissecada, Cristas Residuais e Inselbergs, Vertente Oriental da Serra de Baturité e Serras do Estevão e Falcão, Tabuleiros Pré-Litorâneos e Interiores, Campos de Dunas e Faixa Praial, Planície Fluviomarinha, Planície Fluviais do Rio Choró e seus Principais Tributários, Planície Lacustre e Áreas de Inundação Sazonal,