Evaluation of approximations in modelling the cooling of magmatic bodies

The cooling of a magmatic intrusion is simulated by a simple model of a non-homogeneous earth, with thermal properties depending on temperature, in which heat transfer is assumed to take place by conduction only. The mathematical problem consists in solving a non-linear partial differential equation with continuity conditions on temperature and heat flux imposed at the contacts between different rocks. This has been done numerically by a finite difference method. The model is then adopted as “reality” against which a number of commonly used approximations are tested. It is found that the effect of latent heat liberation can be reasonably taken into account by attributing an effective initial temperature to the magma (errors within 20°C for t > 10⁵ years, when the temperature of the magma is still as high as 600°C); the effective specific heat approximation does not work as well. The dependence of thermal conductivity and specific heat on temperature may be eliminated by maintaining the errors within 30°C for t < 5 × 10⁵ years. The assumption that magma and country rocks have the same thermal properties allows an estimate of the temperature field in the host rocks with errors of 50°C at most. The assumption that all rocks have the same constant conductivity yields results that are far from “reality” (errors of 100–200°C even at shallow depth).     

Structure and components for the emergency response and warning system on Turtle Mountain,Alberta, Canada

Since 2003, a series of over eighty sensors has been installed at Turtle Mountain, site of the 1903 Frank Slide. The purpose of these instruments is to both characterize and provide warning for a second large rock avalanche from the eastern face of the mountain, where various unstable masses have been identified. Although studies continue on the mountain to better understand the deformation patterns and interpretations of the slope kinematics, significant effort has been expended to develop a structure for the warning and emergency response that clearly outlines not only responsibilities and communications protocols during an emergency, but also day-to-day operational responses and procedures to ensure that the system remains operational. From a day-to-day operational perspective, a systematic and repeatable set of procedures is required in order to ensure that not only are data trends reviewed and reported on, but scheduled checks of system functionality are undertaken. An internal Roles and Responsibilities Manual has been developed to clearly outline responsibilities for geoengineering, information technology (IT), and management staff to ensure that system checks are completed and that support is in place on a 24/7 basis should components of the system cease to operate properly or should unacceptable deformations require review. In addition to that, a clear and concise troubleshooting manual has been developed. This document provides simple diagnoses of problems within the system and a clear roadmap of how to fix each component. From a warning and emergency response perspective, a series of color-coded alert conditions has been developed should unacceptable deformations be observed. At each alert level, clear responsibilities for actions and communications have been identified for geoengineering staff, provincial emergency management authorities, municipal officials, and first responders. This has been documented in the emergency response protocol. All documents described here are “living” documents that are updated on a regular basis as changes to the system are made. An annual mock warning exercise has been developed and run in order to test responses to a hypothetical emergency and generate updates to the system documentation.     

Modeling freshening time and hydrochemical evolution of groundwater in coastal aquifers of Shenzhen,China

This work investigated the freshening time and hydrochemical evolution of coastal groundwater in two brackish aquifers in Shenzhen, China. One was the brackish aquifer that resulted from heavy pumping, and the other was the aquifer reclaimed from the coastal sea. Freshening time and hydrochemical evolution of brackish aquifers were quantitatively evaluated using PHREEQC 2.0, a one-dimensional reactive-transport model. Freshening time was shown to mainly depend on pore water velocity, while the chemical composition of groundwater was determined by the cation exchange capacity of the aquifer. It was shown that after heavy pumping ceased, the freshening time for the original coastal aquifer ranged from 20 to over 80 years. While for the coastal reclaimed aquifer, the freshening time was from 85 to 140 years, which depended on the hydraulic conductivity of the fill materials in the reclaimed site. During aquifer freshening, groundwater evolved from Na–Cl type to Ca–Mg–HCO₃ or Na–HCO₃ type. A sensitivity analysis showed that the freshening time was most sensitive to the pore water velocity in the aquifer, while the groundwater chemical composition was most sensitive to the values of cation exchange capacity of the aquifer. As for the dispersivity, it had almost no effect on the freshening time and the chemical composition of groundwater.     

Earthquake imprints on a lacustrine deltaic system: The Kürk Delta along the East Anatolian Fault (Turkey)

Deltas contain sedimentary records that are not only indicative of water‐level changes, but also particularly sensitive to earthquake shaking typically resulting in soft‐sediment‐deformation structures. The Kürk lacustrine delta lies at the south‐western extremity of Lake Hazar in eastern Turkey and is adjacent to the seismogenic East Anatolian Fault, which has generated earthquakes of magnitude 7. This study re‐evaluates water‐level changes and earthquake shaking that have affected the Kürk Delta, combining geophysical data (seismic‐reflection profiles and side‐scan sonar), remote sensing images, historical data, onland outcrops and offshore coring. The history of water‐level changes provides a temporal framework for the depositional record. In addition to the common soft‐sediment deformation documented previously, onland outcrops reveal a record of deformation (fracturing, tilt and clastic dykes) linked to large earthquake‐induced liquefactions and lateral spreading. The recurrent liquefaction structures can be used to obtain a palaeoseismological record. Five event horizons were identified that could be linked to historical earthquakes occurring in the last 1000 years along the East Anatolian Fault. Sedimentary cores sampling the most recent subaqueous sedimentation revealed the occurrence of another type of earthquake indicator. Based on radionuclide dating (¹³⁷Cs and ²¹⁰Pb), two major sedimentary events were attributed to the ad 1874 to 1875 East Anatolian Fault earthquake sequence. Their sedimentological characteristics were determined by X‐ray imagery, X‐ray diffraction, loss‐on‐ignition, grain‐size distribution and geophysical measurements. The events are interpreted to be hyperpycnal deposits linked to post‐seismic sediment reworking of earthquake‐triggered landslides.     

Numerical modeling of a strong dust event over the south China region in March 2010

The mesoscale model WRF-Chem was used to simulate a severe dust storm event that occurred in March 2010. The storm affected a vast area of East Asia, including the south China region and Hong Kong. This southern region is rarely affected by dust weather. The performance of the WRF-Chem was evaluated by observational data such as the National Center for Atmospheric Research reanalysis data for atmospheric circulation, PM10 concentration from various ground stations, and satellite images of Moderate Resolution Imaging Spectroradiometer and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations. The dependence of the model’s performance on certain important parameterizations was examined in this study. For this particular dust storm event, the model results suggest that the simulation is not very sensitive to certain key physical parameterizations such as threshold wind speed of dust emission and the choice of land surface model. In general, the WRF-Chem is capable of capturing the key physical processes for this severe dust event. The analysis of the dust transport fluxes suggests that the dust transport to the south China region is mainly from the north, although there is a mountainous region in the northern part of the south China region.