A summary of sulfur dioxide emission rate measuremnts from Guatemalan volcanoes

Measurements of the sulfur dioxide (SO₂) emission rate from three Guatemalan volcanoes provide data which are consistent with theoretical and laboratory studies of eruptive and shallow magma chamber processes. In particular, unerupted magma makes a major contribution to the measured SO₂ emission rates at Santiaguito, a continuously erupting dacitic volcanic dome. Varying shallow magma convection rates can explain the variations in SO₂ emission rates at Santiaguito. At Fuego, a basaltic volcano currently in repose, SO₂ emission rate measurements are consistent with a high level magma body that is crystallizing and releasing volatiles. At Pacaya, a continuously erupting basaltic volcano, recent SO₂ emission rate measurements support laboratory simulation studies of strombolian eruptions; these studies indicate that the majority of gas escapes during eruptions and little gas escapes between eruptions.Average SO₂ emission rates over the last 20 years for Santiaguito, Fuego and Pacaya are 80, 160 and 260 Mg/d, respectively. On a global scale, these three volcanoes account for 1% of the annual global volcanic output of SO₂. Santiaguito and Pacaya, together, emit 6% of the total annual SO₂ emitted by continuously erupting volcanoes.Even though SO₂ measurements at these volcanoes have been made infrequently and by different investigators, the collective data help to establish a useful baseline by which to judge future changes. A more complete record of SO₂ emission rates from these volcanoes could lead to a better understanding of their eruption mechanisms and reduce the impact of their future eruptions on Guatemalan society.     

The 1999 and 2000 eruptions of Mount Cameroon: eruption behaviour and petrochemistry of lava

Mount Cameroon (4,095 m high and with a volume of ~1,200 km³) is one of the most active volcanoes in Africa, having erupted seven times in the last 100 years. This stratovolcano of basanite and hawaiite lavas has an elliptical shape, with over a hundred cones around its flanks and summit region aligned parallel to its NE--SW-trending long axis. The 1999 (28 March–22 April) eruption was restricted to two sites: ~2,650 m (site 1) and ~1,500 m (site 2). Similarly, in the eruption in 2000 (28 May–19 June), activity occurred at two sites: ~4,095 m (site 1) and ~3,300 m (site 2). During both eruptions, the higher vents were more explosive, with strombolian activity, while the lower vents were more effusive. Accordingly, most of the lava (~8×10⁷ m³ in 1999 and ~6×10⁶ m³ in 2000) was emitted from the lower sites. The 1999–2000 lavas are predominantly basanites with low Ni (5–79 ppm), Cr (40–161 ppm) and mg numbers (34–40). Olivine (Fo_77–85, phenocrysts and Fo_68–72, microlites), clinopyroxene (Wo₄₇En₄₁Fs₁₀ to Wo₅₁En₃₄Fs₁₅), plagioclase (An_49–67) and titanomagnetite are the principal phenocryst and groundmass phases. The lavas contain xenocrysts of olivine and clinopyroxene, which are interpreted as fragments of intrusive rocks disrupted by magma ascent. Major and trace element characteristics point to early fractionation of olivine. The clinopyroxenes (Al₂O₃ 1.36–7.83 wt%) have high Al^iv/Al^vi ratios (1.3–1.8) and are rich in TiO₂, characteristics typical of low pressure clinopyroxenes. Geochemical differences between the 1999–2000 lavas and those from previous eruptions, such as higher Nb/Zr of the former, suggest that different eruptions discharged magmas that evolved differently in space and time. Geophysical and petrological data indicate that these fractionated magmas originated just below the geophysical Moho (at 20–22 km) in the lithospheric mantle. During ascent, the magmas disrupted intrusions and earlier magma pockets. The main ascent path is below the summit, where newly arrived magma degasses. Degassed magma simultaneously intrudes the flank rift zones where most lava is extruded.An erratum to this article can be found at     

Pollution characteristics of alluvial groundwater from springs and bore wells in semi-urban informal settlements of Douala,Cameroon, Western Africa

Alluvial groundwater from springs and bore wells, used as the major source of water for drinking and other domestic purposes in the semi-urban informal settlements of Douala, Cameroon, has been studied. Six representative springs, four bore wells and two hand dug wells, situated in the Phanerozoic basin were selected, from which a total of 72 water samples were analyzed for chemical characteristics and indicators of bacterial contamination. The results showed anthropogenic pollution, evident from high concentrations of organic (up to 94.3 mg NO₃/l nitrate) fecal coliform and fecal streptococcus detected in the springs and bore wells (with values of 2,311 and 1,500 cfu/100 ml, respectively). The pH ranged from 3.4–6.5, which is lower than the guidelines for drinking water. Groundwater samples from background upstream inland natural areas W1 and W2 had low electrical conductivity (54.2 and 74.8 μs/cm, respectively) and major ions, which increased downstream in the valleys, peaking in the more densely settled areas. An acceptable concentration of solutes was observed for the bore wells except for a single sample from B4. The bore-well sample B4 registered the highest microbial content (2,130 cfu/100 ml) and nitrate level(26 mg/l), which could be due to the bottom of this well lying just at or close to the zone of mixing between sewage and groundwater. The absence of a direct correlation between nitrate and fecal matter suggests multiple sources of contamination. The shallow alluvial aquifer consists of unconsolidated deposits of gravel, sand, silt and clay. The springs, therefore, receive direct recharge from the ground surface with limited contaminant attenuation, which leads to water quality deterioration, especially during the rainy season. This shows the urgent need to put basic service infrastructures in place. The local population should be sensitized to the importance of chlorinating and boiling drinking water to prevent health hazards.     

Monitoring the recovery of a previously exploited surf-zone fish community in the St Lucia Marine Reserve,South Africa,using a no-take sanctuary area as a benchmark

Limiting accessibility to a fishing area can reduce fishing effort effectively and may therefore promote local recovery of depleted stocks. In January 2002, beach driving was banned in South Africa, thereby reducing angler access to large areas of the coastline, particularly in less-developed areas. In November 2001 a project had been established in the St Lucia Marine Reserve, on the east coast of South Africa, to compare surf-zone fish populations inside a no-take sanctuary zone with those in an adjacent exploited area. Subsequent to the ban, the aim of the project was adapted such that surf-zone fish populations were monitored for potential recovery in what had been the exploited area, located to the north of Cape Vidal, which anglers could no longer access easily, because of the prohibition on beach driving. Standardised research fishing was conducted at two sites in the previously exploited area and two sites in the no-take sanctuary. Conventional stock-status indicators showed evidence of recovery in the four most common species caught in the previously exploited area, in terms of both abundance and biomass. Generalised additive mixed models were used to account for the influence of targeting specific species; however, subtle differences in habitat between the sampling sites, improved angling skill over time, variability in recruitment, and differential species-specific responses complicated interpretation of results. The implications of the findings are discussed in terms of the future monitoring and management of marine protected areas both within the St Lucia Marine Reserve and farther afield.     

Systematic documentation of landslide events in Limbe area (Mt Cameroon Volcano,SW Cameroon): geometry,controlling, and triggering factors

Limbe town and surrounding areas, on the SE foot slopes of the active Mt Cameroon Volcano, have experienced numerous small-scale shallow landslides within the last 20 years. These resulted in the loss of ~30 lives and significant damage to farmland and properties. Landslides and their scars are identified in the field, and their geometry systematically measured to construct a landslide inventory map for the study area. Specific landslides are investigated in detail to identify site-specific controlling and triggering factors. This is to constrain key input parameters and their variability for subsequent susceptibility and risk modeling, for immediate local and regional applications in land-use planning. It will also enable a rapid exploration of remediation strategies that are currently lacking in the SW and NW regions of Cameroon. Typical slides within the study area are small-scale, shallow, translational earth, and debris slides though some rotational earth slides were also documented. The depletion zones have mean widths of 22 m ± 16.7 m and lengths of 25 ± 23 standard deviation. Estimated aerial extents of landslide scars and volume of generated debris range from 10¹ to 10⁴ m² and 2 to 5 × 10⁴ m³, respectively. A key finding is that most slope instabilities within the study area are associated with and appear to be exacerbated by man-made factors such as excavation, anarchical construction, and deforestation of steep slopes. High intensity rainfall notably during localized storms is the principal triggering factor identified so far. The findings from this case study have relevance to understanding some key aspects of locally devastating slope instabilities that commonly occur on intensely weathered steep terrains across subtropical Africa and in the subtropics worldwide and affecting an ever denser and most vulnerable population.     

Earth Science Education in Cameroon: a case study from the University of Buea

Cameroon is a bilingual country with French and English being the official languages. This bicultural status is linked to pre-independence colonisation of the territory. Consequently, two educational systems exist in formal schools, colleges and the university sector. Studies of Earth Science Education curricula in these systems show completely divergent approaches in colleges and at the Tertiary level. An assessment of the factors that influence these divergences shows their relationship to the cultural background and to available expertise. From 1962 to 1992, Earth Science Education at the Tertiary level was limited to the unique University of Yaoundé and was based on the French system, even though the University served both systems. The curriculum was not related to the major priority needs of the country with respect to its natural or mineral resources and this handicap is being felt today. However, the creation in 1993 of six independent government universities in the country, with one — the University of Buea — being of an ‘Anglo-Saxon’ tradition, has resulted in the development of varied curricula in Earth Science Education in five of these universities. The varied approach is aimed at meeting manpower needs in priority areas of the subject in future. A comparison of the Earth Science curricula from 1993 to 1998 in the Universities of Yaoundé I, Douala and Buea is used to identify the divergent approaches and the expected advantages of each curriculum. A more detailed evaluation of the curriculum in the University of Buea is used to highlight the attempt being made to train geoscientists who will be capable of exploiting the natural resources of the country and equally ensure the conservation of the environment for future generations.     

Molecular research on the systematically challenging smoothhound shark genus Mustelus: a synthesis of the past 30 years

The species-rich genus Mustelus (smoothhounds) of the shark family Triakidae is one of the most bio-economically important groups of elasmobranchs in the world’s oceans. Despite the commercial value of Mustelus, the systematics of the group remains largely unresolved and there is no global review or synthesis of knowledge about the conservation status and conservation genetics of smoothhounds across all oceanic regions. Here, we analysed published studies as well as grey literature to gain insight into the biogeographic, ecological and behavioural factors that shape genetic diversity in smoothhounds, and we identify critical knowledge gaps. From a series of molecular phylogenetic studies it can be inferred that the genus Mustelus is paraphyletic and that the aplacental species evolved secondarily from the placental species of the genus. The increasing availability of genetic data aids in disentangling systematic issues, such that more meaningful morphological characters can be chosen for use in practical field-identification keys for co-occurring smoothhounds. An integrative taxonomic approach to the genus Mustelus may offer the best chance of recording and protecting the biodiversity of these sharks. Furthermore, it is evident that different smoothhound species exhibit unique gene-flow patterns, suggesting varying rates within species and hence that species-level conservation approaches would be most appropriate. Molecular studies have advanced our understanding of smoothhound biology (including reproductive traits), ecology and evolution. While many knowledge gaps remain, a crucial lesson from this review is that, when doing assessments on a molecular level, it is important to place genetic results in a broader context, by assimilating biological and ecological data, if definitive conclusions are to be drawn.