Social Geology and Landslide Disaster Risk Reduction in Sri Lanka

AbstractLandslide disaster risk reduction is presently a challenging task facing by Sri Lankangeologists. Increasing trend of population growth in Sri Lanka has adversely affected thestability of central highland due to various human activities. Among them establishment ofhuman settlements and change in land use pattern have become a serious issue in triggeringland instabilities in central highland of the country. National Building Research Oragnisationwhich is the main focal point in land slide disaster risk reduction in Sri Lanka has takenvaluable and timely needed actions including preparation of landslide hazard zonation maps,early warnings and mitigations. Though the landslide is a geological phenomenon, it is highlyinteracted with human societies. Hence managing the issues arising with the landslideoccurrence should be addressed with a sociological approach. This new approach is known asSocio Geological approach which is discussed here.Key words: Landslide, Geology, Socio Geology, Social Geologis

Caves and karst-like features in Proterozoic gneiss and Cambrian granite, southern and central Sri Lanka: An introduction

There has been little study of the geology and geomorphologyof the caves and karst-like features developed in the Proterozoicgneiss and Cambrian granite of Sri Lanka. This lack of studyis surprising given that caves and rockshelters in these rockscontain significant archaeological and cultural sites. Caves andkarren, both mimicking those developed in carbonate rocks,have formed both in gneiss, which is the dominant rock type ofthe Proterozoic crust of the island and in granite. In addition tooverhangs, boulder caves, soil pipes and tectonic caves, tunnelcaves, arch caves and block breakdown caves of significant sizeare developed in siliceous rocks in Sri Lanka. While metamorphoseddolomites are interfoliated within the gneissic suite,simple removal of carbonate by solution from within the surroundingrock cannot account for all or most of the speleogenesisobserved. While spalling and breakdown are responsiblefor cave enlargement cave initiation is probably due to eitherphreatic solution of silicates and/or phantom rock processes.Speleothems and cave minerals including silicates, phosphates,gypsum, carbonates and niter are found in the caves. Activesilicate speleothems are not restricted to joints and fissures andsuggest that solution of silicates is currently occurring withinthe body of the rock in the vadose zone. While guano is thelikely source of the phosphate, sulfate and nitrate, the sourceof the calcium in the carbonates remains unclear. Caves in theintrusive and metamorphic rocks of Sri Lanka are enigmatic.They are unexpectedly similar in appearance to their carbonatekarst counterparts. Continuing research will allow them tohold a mirror to our understanding of speleogenesis, mineralizationand sedimentation in carbonate karst caves

Landslide and Subsidence Potential due to the Progressive Development of Cave Network in Ella-Wellawaya Area, Sri Lanka

Carbonate rocks are highly soluble. Sinkholes are formed by both the failure of solution cavities andthe rapid removal of fines from solution cavities in carbonate and metacarbonate rocks. Sri Lankanlandmass is composed of Proterozoic high-grade metamorphic rocks such as gneiss andmetacarbonates like marble. Large caves in Sri Lanka form in both marble and gneiss. A few landsubsidence events have occurred recently in Ella-Wellawaya area, which is a hilly terrain. In addition,some cases of groundwater table lowering, which has caused drying of dug wells have also beenrecorded within the area, apparently related to a major development project presently under way in thearea.The main objective of this paper is to draw the immediate attention of local researchers andauthorities whom are working on mitigation and management of disasters, groundwater and climatechange, showing the importance of carrying out detail studies on potential landslides and landsubsidence of Ella-Wellawaya area for avoiding and minimising loss of humans and properties.Preliminary surveys on some land subsidence cases and speleological studies including geology,hydrogeology and morphological mapping of the underground caves in the area have been activelycarried out. According to the results, it is shown that the subsidence is likely to be correlated with thecollapsing of cavities and weathered zones in metacarbonates, and disturbances to the groundwatertable. Field explorations done during the last two years have discovered several large undergroundcaves in the area some more than 100 m across. Most of the cave roofs have been thinned by thebreakdown of bedrock along weak zones such as joints. Since the process of collapse, trigged byweathering is continuing and patches and lenses of carbonate rocks observed in the caves are stillbeing dissolved, the expansion of the cave spaces is unending. Some of the chambers of these cavesare aligned parallel to the steep slopes in the Ella-Wellawaya area and some acted as undergroundwater conduits and storages during the rainy seasons. The Ella-Wellawaya area has been undergone achange in vegetation cover since the colonial period and hence the area is more prone to soil erosionwhich exposes the near surface natural cavities to the underground caves. Present human exposuresand interactions within the susceptible slopes have brought lives and properties under threat. Hencefuture land subsidence and landslide occurrences are highly predictable with the recent conditions inthe area and hence threat to human life and properties is high. The tourism industry, unique to the areacould particularly be affected. Hence such hazardous should properly be identified and demarcatedand the erosion triggered by present vegetation changes must properly be addressed.Keywords: Metacarbonate rocks, Subsidence, Ella-Wellawaya, Cave network, Erosio

Geochemistry and SIMS U-Pb zircon geochronology of the Vijayan anatectic melts of eastern Sri Lanka.

Session T33.P5 - The Proterozoic Earth - paper no. 3728Sri Lanka comprises three roughly north-south trending lithotectonic complexes, from west to east the Highland Complex, the Wanni Complex, and the Vijayan Complex. They are made up of amphibolite- to granulite-facies metamorphic rocks. The origin of these complexes is not well-established, and correlations can be tested by comparing their geochemistry, age, and isotope signatures with other well-known tectonic units. Timing, geochemistry and pressure-temperature (P-T) conditions of the western metamorphic complexes have been previously studied, and reported by numerous workers as summarized in Santosh et al. [1]. The Highland Complex has been interpreted as a stable fragment of the Columbian supercontinent, while it is suggested that the Wanni Complex is a volcanic arc terrane accreted while in proximity to the terranes of East Africa [2][3]. Meanwhile, the origin of the Vijayan Complex is still mysterious. Geological research on this part of Sri Lanka has been hindered by civil war. Although geochronological and geochemical data of the metamorphic basement are now available [4], these data are not sufficient to reveal its origin. This poster reviews data obtained by previous workers, and provides new preliminary geochemical data as well as SIMS U-Pb zircon ages, suggesting that the geochemistry and age signatures of the anatectic melt generated during Vijayan Complex metamorphism may be more meaningful than previously thought. The associated granitic anatectic melts are biotite- and hornblende-bearing. The mineral assemblage is typical for I-type granite in a broad sense. This association is supported by geochemical and positive Nd isotopic data. However, two series of anatectic melts are identified in our samples from the Vijayan Complex. One is the ordinary metaluminous to weakly peraluminous I-type granite or granodiorite, which are dated within the widely reported age range of 1100-1050 Ma [4]. The other one is solely metaluminous granodiorite, which has a higher high field strength elements (HFSE) content. Some of these latter granodiorites contain zircons that include a significant 550 Ma age population, which could be related to metamorphism associated with the Pan-African orogeny. Our preliminary SIMS U-Pb zircon ages suggest some of these granodioritic bodies in the southern Vijayan Complex also indicate a protolith age of 790 Ma, which has not been thoroughly discussed in previous literature. Apparently, these bodies are restricted to the controversial Highland-Vijayan mixing zone of the western Vijayan Complex. Similar results have been obtained for the Wanni Complex and potentially related terranes in East Africa. Continuing research on these melts might redefine the boundary of the Vijayan Complex, provide further clues to the origin of the Vijayan Complex, and refine its relationship with the Highland Complex. References: [1] Santosh M et al. (2014) Precambrian Research 255(1): 1-29 [2] Kehelpannala KVW (2004) Gondwana Research 7(4S): 41-46 [3] Kröner A et al. (2003) Journal of Asian Earth Sciences 22(3): 279-300 [4] Kröner A et al. (2013) Precambrian Research 234(1): 288-32

Microbiological study in a gneissic cave from Sri Lanka, with special focus on potential antimicrobial activities

The emergence of antibiotic resistance is a global health crisis, thus the search for novel antimicrobial compounds has become a continuous necessity. Underexplored and extreme environments, such as cave ecosystems, have been identified as a promising potential source for the discovery of novel microorganisms with novel antimicrobial compounds (AMC). This study presents the first cave microbiological investigation in Sri Lanka, with a special preference for bioprospecting of novel AMC. The cave sediment characterization demonstrated the presence of close to strong acidic conditions (pH 3.1 – 3.3) and thus indicates the possibility of isolating acidophilic microorganisms. Eight cave wall/ceiling fungal strains were isolated from Sthreepura Cave - Kuruwita and identified using both morphological and ribosomal Internal Transcribed Spacer (ITS) region sequence analysis. Interestingly, four fungal isolates (Penicillium panissanguineum, P. cremeogriseum, Aspergillus bertholletius and Trichoderma yunnanense) were found to be the first records in Sri Lanka. Of these eight isolates, three showed antimicrobial activity (AMAs) against at least one of the five tested human pathogens in preliminary screening, while A. fumigatus (SKW 404) strain showed the highest AMA against Staphylococcus aureus (ATCC 11778) assessed by agar culture plug method on Muller Hinton Agar (MHA). Crude Ethyl Acetate (EtOAc) fraction of both mycelial and Potato Dextrose Broth (PDB) extracts of A. fumigatus demonstrated similar bioactive metabolic profiles with four corresponding chemical fractions [Rf = 0.47, 0.56, 0.65, 0.82; EtOAc: Hexane (4:1, v/v)] in TLC: agar overlay bioassay. The present study indicates that there is potential for discovering novel Sri Lankan deep cave microorganisms and bioprospecting of their novel bioactive compounds. Hence, further island-wide in-depth cave microbiological investigations are required for a better understanding of the Sri Lankan cave microbiology