Chemical character of return irrigation water in tropical volcanic islands

Unequivocal identification of irrigation return water through routine chemical analyses does not appear possible in tropical volcanic islands. Several constituents, nevertheless, will suggest an agricultural source if they are present in large concentrations. Nitrate is the most useful indicator; background concentrations are generally less than 2 ppm but return irrigation water will commonly have concentrations of between 5 and 50 ppm. Sulfate appears to be the next most useful indicator. Calcium, silica, and bicarbonate have also been reported to be significant. Where detailed studies have been made of agricultural water balances, regional ground-water flow directions, and deep-well hydraulics, hydrochemistry can provide critical supporting data for the identification of return irrigation water which could be a potential ground-water pollutant.     

Recent Improvements to IERS Bulletin A Combination and Prediction

Driven by a need for increased accuracy in real-time Earth orientation parameters (EOPs), the Bulletin A (Rapid Servce and Predictions) of the International Earth Rotation Service (IERS) has recently made several major changes to its combination and prediction procedures. Changes to the process ob combining multi-technique results include creation of a daily Bulletin A updata, inclusion of several new data sets, and use of polar motion rantes for the latest epoch. Notably, the contributions from GPS observations have grown steadily in significance, both for polar motion and Universal Time (UT1). The prediction procedure has, in turn, benefited from these changes as well as improvements to the polar motion prediction model. As a result, demanding real-time applications, such as for satellite orbit extrapolations should observe a major improvement in the accuracy of our real-time EOP products. All results, together with supporting and diagnostic information, are available at the website http://maia.usno.navy.mil. The maximum EOP errors (root-mean-squared sense) that a real-time user would experience using the latest available update of Bulletin A are currently estimated to be ∼0.9 milliarcseconds (mas) for polar motion and ∼0.15 milliseconds (ms) for UT1-UTC. The data latency (the lag since the most recent observations) for EOP predictions need not exceed ∼41 hours for users who avail themselves of the daily updates. Over the past four years, the accuracy for real-time applications has improved by nearly a factor of 4 in polar motion and a factor of 10 in UT1. This is primarily due to the large reduction in data latency, which in turn is mostly possible due to the Rapid product delivery of the International GPS Service (IGS) (see Mireault et al, 1999). ? 2001 John Wiley & Sons, Inc.     

Measuring Flume Surfaces for Hydraulics Research Using a Kodak DCS460

A critical problem in hydraulics research is accurate measurement of fluvially worked sediments, both in the field and in scaled representations of field situations in laboratory flumes. Such measurement must provide information on individual grain characteristics, and their organisation into structures referred to as bedforms. Existing measurement approaches are based upon mechanical or laser profiling devices, which are both expensive and take considerable time to acquire data, particularly where information is required at very high densities. This paper demonstrates how conventional automated terrain model extraction software, combined with image acquisition using a Kodak DCS460 digital camera, has been effective in generating digital elevation models of complex bed morphology. This has reduced time spent collecting data in the flume and has allowed data collection at much higher spatial and temporal densities. Application of the method is illustrated by research carried out at Hydraulics Research Wallingford. Issues discussed include configuration of photographs and control coordinates; appropriate camera calibration methods; stability of inner orientation of the Kodak DCS460; and accuracies obtained. Comparisons with independent check data reveal that accuracies of ±2.5mm have been achieved using a camera-to-object distance of 4.2 m.     

Precipitation interception in Australian tropical rainforests: I. Measurement of stemflow,throughfall and cloud interception

Methods for measuring throughfall, stemflow and, hence, interception in the tropical rainforests of the Wet Tropics region of North Queensland, Australia, were tested at three sites for between 581 and 787 days. The throughfall system design was based on long troughs mounted beneath the canopy and worked successfully under a range of rainfall conditions. Comparison of replicated systems demonstrated that the methodology is capable of capturing the variability in throughfall exhibited beneath our tropical rainforest canopies. Similarly, the stemflow system design which used spiral collars attached to sample trees worked well under a range of rainfall conditions and also produced similar estimates of stemflow in replicated systems. Higher altitude rainforests (>1000 m) in North Queensland can receive significant extra inputs of water as the canopy intercepts passing cloud droplets. This additional source of water is referred to as ‘cloud interception’ and an instrument for detecting this is described. The results obtained from this gauge are compared with cloud interception estimates made using a canopy water balance method. This method is based on stemflow and throughfall measurements and provides an alternative means to fog or cloud interception gauge calibration techniques used in the literature. Copyright © 2007 John Wiley & Sons, Ltd.     

1989–1995 Earthquake sequences in the Galeras volcano region,SW Colombia,and possible volcano–earthquake interactions

The Galeras volcanic complex, located in the Nariño department, SW Colombia, includes the most historically active volcano in the country, Galeras, a 4276 m high stratovolcano located 9 km west of the city of San Juan de Pasto (400,000 inhabitants). The area is also affected by the continental faulting represented by the Buesaco, Aranda and Pasto faults belonging to one of the most seismically active structures in Colombia, the Romeral fault system. Several moderate to strong shallow earthquakes affected the city of San Juan de Pasto and its neighbouring region since the XVII century. The coexistence of an active volcanic complex and an active fault system complicates the study and interpretation of the different processes taking place in the region as well as the identification of any connection or interaction among them.The reactivation of the volcano in 1989 was characterized by three main magmatic events: (1) a series of Vulcanian eruptions during 4–9 May 1989, with semi-continuous ash emissions from a secondary crater; (2) the emplacement of an andesitic lava dome at the bottom of the main crater from September 1990 until December 1991; and (3) six Vulcanian eruptions from the main crater during 1992–1993, with destruction of most of the dome during the first one on 16 July 1992. During the same period, four earthquake sequences were located in a limited area N and NE of Galeras volcano on August–September 1989 (AUG1989), April–June 1993 (APR1993), November–December 1993 (NOV1993) and March–August 1995 (MAR1995). The last one included a Ml4.7 main shock on 4 March 1995 producing moderate to high damage in the epicentral region (MSK maximum intensity VIII), and in the city of San Juan de Pasto (VI–VII). The last damaging earthquake in the region was a MSK-intensity VIII–IX in 1947.A detailed analysis of the spatio-temporal characteristics of the four earthquake sequences allowed identifying their different origin and suggesting some interrelationship between the reactivated eruptive process and the contemporaneous seismic activity. The AUG1989 sequence presents a typical volcanic swarm-like pattern most probably related with the process of magma intrusion from depth at the beginning of the volcano's reactivation. The APR1993, the NOV1993 and the MAR1995 sequences show a clear tectonic origin with events occurring on rupture planes almost vertical that can be associated to the active faults in the area, The seismogenic process of these three sequences could have been activated or accelerated by the main eruptions during 1992–1993.These results suggest that constrains provided by improved relocations and the detailed analysis of the space–time characteristics of earthquake sequences in Galeras volcanic environment allow to establish the different generation mechanisms involved and to suggest feasible explanations on the possible interrelationships of the magmatic–volcanic processes and the seismicity observed.