NS31B-01
Fires in Operating or Abandoned Coal Mines or Heaps of Reactive Materials and the Governing Transport and Reaction Processes
Spontaneous combustion is a world wide problem for technical operations in mining, waste disposal and power plant facilities. The principle driving the combustion is every where the same independent of the different reactive materials: Fresh air with the common oxygen content is getting in contact with the reactive material by human operations. The following reaction process produces heat at a usually low but constant rate. The reactive material in operating or abandoned coal mines, heaps of coal, waste or reactive minerals is most times strongly broken or fractured, such that the atmospheric oxygen can deeply penetrate into the porous or fractured media. Because the strongly broken or fractured medium with air filled pores and fractures is often combined with a low thermal conductivity of the bulk material the produced heat accumulates and the temperature increases with time. If the reactivity strongly increases with temperature, the temperature rise accelerates up to the "combustion temperature". Once the temperature is high enough the combustion process is determined by the oxygen transport to the combustion center rather than the chemical reactivity. Spontaneous combustion is thus a self- amplifying process where an initial small variation in the parameters and the starting conditions can create exploding combustion hot spots in an apparently homogenous material. The phenomenon will be discussed by various examples in the context of the German - Sino coal fire project. A temperature monitoring in hot fracture systems documents the strong influence of the weather conditions on the combustion process. Numerical calculations show the sensitivity of the combustion to the model geometries, the boundary conditions and mainly the permeability. The most used fire fighting operations like covering and water injection are discussed. A new method of using saltwater for fire fighting is presented and discussed. References: Kessels, W., Wessling, S., Li, X., and Wuttke, M. W. Numerical element distinction for reactive transport modeling regarding reaction rate. In Proceedings of MODFLOW and MORE 2006: Managing Groundwater Systems, May 21 - 24, 2006, Golden, CO USA (2006). Kessels, W., Wuttke, M. W., Wessling, S., and Li, X. Coal fires between self ignition and fire fighting: Numerical modeling and basic geophysical measurements. In ERSEC Ecological Book Series - 4 on Coal Fire Research (2007). Wessling, S., Litschke, T., Wiegand, J., Schlömer, S., and Kessels, W. Simulating dynamic subsurface coal fires and its applications. In ERSEC Ecological Book Series - 4 on Coal Fire Reserach (2007). Wessling, S., Kessels, W., Schmidt, M., and Krause, U. Investigating dynamic underground coal fires by means of numerical simulation. Geophys. J. Int. (submitted).
NS31B-02
Assessment Ground Safety Using Time Lap Vertical Gravity Gradient At The Subsidence Area
We have carried out time-lap vertical gravity gradient (VGG) survey in order to assess the ground safety before and after grouting. The target area is new pavement through the rice field, and the area has subsidence problems because of excessive pumping for agricultural irrigation. Therefore, it has been reinforced with cement grouting avoiding subsidence. In this paper, we examined the change of subsurface density distribution due to cement grouting by means of VGG survey. VGG method is more sensitive to detect the change of near surface than gravity survey itself because VGG enhanced small variation of gravity anomaly. We gathered one line gravity data about 270m long at every 2m. VGG survey consisted of observations between the ground bottom and the top separated vertically about 1.5m with help of the ladder specially designed. According to result, VGG anomaly made the response of man-made waterway clearer than Bouguer anomaly in the middle part of the line. And VGG result showed changes of subsurface density distribution after grouting.
NS31B-03
Spatial and temporal vegetation change in Southern Brazilian Amazon using GIS and NOAA /AVHRR data
Over the past two decades, environmental alteration in the Amazon Basin due to land development, population
increase, and the consequent deforestation, has become a serious ecological problem in this region known to
be, both climatologically and biogenetically, one of the most important regions in the world.
In Mato Grosso, the Brazilian state with the highest deforestation rate, vegetation cover change has been reported
to occur over large areas due to the introduction of large-scale mechanized agriculture, extensive cattle ranching
and slash-and-burn cultivation.
Spatial and temporal land cover (vegetation) change is noted to potentially set up temperature increase and
rainfall decrease. We stress on the importance of vegetation change information as crucial inputs for eco-climatic
analysis of these spatial patterns of change and their temporal trend at local scale, as well as for real-time
monitoring or detection of the deforestation events for appropriate action by the Brazilian government.
In this study, Principal Component Analysis (PCA) is performed onto NOAA AVHRR remote-sensed and multi-
spectral data covering the 1981-2003 period, using GIS. Our investigation focuses on developing a vegetation
quantification algorithm for change detection in the vegetation cover over every few years, using the PCA first
component, which is shown to characterize the overall vegetation cover types. Land cover features and their
spatio-temporal change over the Southern Brazilian Amazon are analyzed and discussed, and their relationships
with global and regional eco-climatic phenomena is highlighted.
http:www.agu.org/sanga1
NS31B-04
The Importance of the Free Surface to Magmatic Plumbing Features
We wish to call the attention of the near-surface community to the need for geophysical sensing methods that can evaluate rock properties in the upper ~100 m to aid in the understanding and prediction of volcanic eruptions. Both field observations and numerical models show that decrease of confining stress as the free surface is approached can interact with different host rock properties to have a profound effect on the style of the early stages of a volcanic eruption. For example, at Paricutin where the host rocks were relatively strong basalts, eye witness accounts of the initiation of the eruption indicate that the crack tip that led the ascent of magma was a single, long fracture filled with gases well ahead of magma. On the other hand, observations from a slightly exhumed Miocene basaltic neck in southern Nevada show anastomosing of the magma with the country rock as it approached the surface through a weak and fractured rhyolitic tuff, resulting in a widening of the dike at 50-100 m depths and flaring at shallower depths. In the absence of observations of the initial eruption at the Nevada site, and of subsurface geology at Paricutin, any contrast in subsurface styles must still be speculative. Still, a contrast is supported by numerical models that show magma distributing itself among multiple paths to the surface as it rises through a mass of blocks. Models of conduit erosion by overpressured multiphase flow show similar flaring at the surface. Geophysical sensing methods that could penetrate beneath the scoria cones of historical eruptions to identify such structures would be very helpful in understanding how pre-eruptive geology controls near-surface magmatic plumbing. Sensors that could determine near-surface mechanical properties such as fracturing, low-frequency elastic moduli and porosity would be useful in predicting initial eruptive styles.
NS31B-05
Geophysical Monitoring of CO2Injections in Decimetric Limestone Samples
Within the framework of the fight against greenhouse gases emissions, one of the adopted solutions is the carbon dioxide sequestration. Injections of this gas in underground reservoir will acidify the fluid saturating the pores of the rock, which can then react with the porous matrix. The fluid-rock interactions consisting on both dissolution and precipitation reactions may modify porosity and permeability of the reservoir. Monitoring, during the injection and storage phase, will be required to detect possible leaks through the geologic strata overlaying the reservoir or modifications of its hydraulic properties. Among the available monitoring methods, geophysical techniques appear particularly adapted. In order to quantify the effect of dissolution reaction on the geophysical observables, we performed laboratory experiments on decimetric limestone samples (10 cm diameter and 30 cm length). A CO2saturated fluid percolated throughout the sample. During the experiments the core is placed into an original percolation device allowing to measure in situ and continuously different physical parameters (permeability, pH, electrical conductivity of both rock and fluid) during the solution flow through a sample. The output fluid was regularly sampled and the fluid chemical composition was analyzed. In addition, the P- and S-waves velocities and attenuations were measured along the sample (each centimeter) regularly. The results of the experiments, where a limestone reacts with CO2saturated reactive fluid (pH=4), reaching a one order of magnitude permeability increase, show that the seismic waves velocity and attenuation measurements allow us to follow the evolution of the porosity along the sample. The 3% increase of the porosity and the creation of preferential flow paths (wormholes), detected by the seismic study, are in agreement with the X-ray Computed Tomography (CT), the variations of the electrical formation factor, and the chemical analyses of the output fluid.
NS31B-06
Subsurface Hydrological Monitoring of a Watershed with Hybrid Sensor Networks
This abstract describes novel instrumentation for in situ hydrological monitoring of watersheds. Our system
autonomously measures various attributes of the watershed soil, including chemical composition, moisture,
temperature, and resistivity. The measurements are taken at several depths and are communicated to a
processing server over the existing GSM cellular infrastructure.
Existing hydrological methods suffer from shortcomings in accuracy, resolution, and scalability. Their fragility,
high power consumption, and lack of long-range communication capability necessitate frequent site visits by
experts. Cabling requirements and large size limit their scalability and make such systems prohibitively
expensive.
Our system is comprised of a network of sensor strings, each of which connects up to 100 sensing nodes on a
communication line that can be up to 100m in length. Each of the nodes is comprised of the sensors needed for
measuring soil attributes of interest, as well as a microcontroller with basic communication and processing
capabilities. A relay point at the surface aggregates data from the nodes and wirelessly transmits it to a base
station that serves as a gateway to the outside world. The base station aggregates data from multiple strings and
utilizes the GSM cellular infrastructure to communicate the data to a data collection server, and to receive remote
updates to be downloaded to the sensor strings. Ultra-low power design and remote maintenance result in an
unattended field life of over 5 years.
The system is scalable in area and sensor modality, as covering a larger area would only entail additional sensor
strings, and the nodes are designed to facilitate the interfacing of additional sensors. The system is robust, as
the only exposed portion is the relay point. Data collection and transmission can be event-driven or time-driven.
Battery power, which can be supplemented with solar harvesting, and wireless short- and long-range
communication, eliminate the need for surface wiring and significantly reduce the cost of system deployment.
Currently, our estimate is a cost of less than $30 for each sensor string for small batch production, which
compares very favorably to existing systems that have limited capabilities yet cost tens of thousands of dollars.
In summary, we believe that the proposed system has the potential to significantly improve hydrological
monitoring. The system enables the collection of data at a scale and resolution that is orders of magnitude
greater than any existing method, while dramatically reducing the cost of monitoring. The quality and sheer
volume of information collected as a result will enable previously infeasible research in hydrology.
http:web.umr.edu/~jrk4y8
NS31B-07
Human ecology, land use and biomass burning in DRC, Central Africa, using GIS and remote-sensing
Four major vegetation types are shown to be the dominant ecosystems over Kayamba County in the Congo
(DRC). Covering about 76.6% of the County total area, savanna is the largest land cover type, and the
marshlands (grass formations over waterlogged soils) the second (12.9% of the area). This amounts to 89.5%
of the County lands being covered with herbaceous vegetations, compared to a very weak proportion of forests
cover (10.5%). Open water bodies are rare, covering only 1.1 km2 (0.04%) of the County territory. They consist
mostly of small ponds in the vast marshlands along the main rivers. Kayamba is thus shown to be a savanna
area, with large expanse of wetlands and scattered patches of various types of tropical rainforests (natural
or man-made forests, and sparse woodlands).
Rain fed agriculture (slash and burn in the forests, or shifting cultivation in the savanna) is shown to be the main
life-sustaining human activity among the Luba of Kayamba County. Its full dependence on the natural elements
(especially the rainfall) makes it easily affected by any variability in the climatic regimes. Hunting, fishing and
gathering provide a supplement to the daily food intake. This lifestyle compares to that of other tropical rainforest
dwellers (e.g. the Kayapo Indian in Brazil or the Karen in Thailand). A strong village dynamics (permanent
relocations in the North and the Center, new villages built at important crossways, or splitting followed by
relocation along main arteries in the South), more likely in response to the need for a new economy-oriented way
of life in the County is also observed, pointing to the need for more investigation in relation with the possible
development of this area.
Biomass burning in Kayamba is either planned (bushfire hunting) or accidental (uncontrolled fires from field
debris burning), occurring exclusively during the peak of the dry season (June-July). The seasonal bushfires
regime is analyzed and discussed. It is shown that of the annual GHG emissions into the atmosphere, 615,000
tCO2⋯ (99.6%) are from bush fires, and the remaining 3,206 tCO2⋯ from fuel wood burning.
This amounts to about 13,612 tCO2⋯ for every one of the 45,000 inhabitants of the County.
http:www.agu.org/sanga2
NS31B-08
Probing and Monitoring the Active Layer of Permafrost in Deception Island (Antarctica)
During the last years, our group has established a complete set of experiments with the goal of monitoring the thermal and depth variation in the active layer in the surrounding area to the Spanish Antarctic Station Gabriel de Castilla located in Deception Island (South Shetlands archipelago.Antarctic). The initial campaigns were addressed to measure meteorological parameters such as; air and soil temperature and humidity, solar and infrared radiation and wind speed and azimuth in summer periods. These initial efforts have permitted to define areas of special interest where a complete study of the active layer depth and the permafrost distribution has been performed. Nowadays, a protocol CALM site located close to Crater Lake is maintained and data about active layer depth and ground temperature are continuously recorded.