Collapse at illegal gold mine kills six in Jambi Province, Sumatra.

Six people have been confirmed dead following a collapse at an unlicensed gold mine in Jambi Province, Sumatra, on Sunday 22 December 2019. The incident happened at about  1.00 pm local time in the village of Pulau Baru following heavy rains in the area. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. One of the deceased has been identified as a local man, the other five are reported to have come from Central Java. Unlicensed mining operations in Indonesia are notoriously unsafe, and also cause a variety of environmental problems associated with indiscriminate digging, with some mining haven taken place inside national parks.

Rescue workers at the scene of a mine collapse in Jambi Province, Sumatra, on 22 December 2019. Basarnas.

The site on which the mine was operated had apparently been leased from a local landowner for the purpose if mining by two businessmen, who's identities have not been released for legal reasons while there is an ongoing investigation. The mineworkers were apparently using mercury to extract gold from ore at the site, a process in which ore is mixed with mercury to remove the gold, then the resulting amalgam of the two metals burned to remove the mercury, effectively evaporating it off, resulting in large amounts of fumes. There are means of extracting gold from ore without mercury, but this is the simplest method on a low technology base. Mercury is a highly potent neurotoxin, and can cause a variety of other health and developmental problems in children; it is considered to be particularly harmful to infants and fetuses. The fumes are persistent in the atmosphere and can travel long distances, which places those not directly involved in the amalgamation process at risk, since the process is often carried out in residential areas, and close to streams from which drinking water is extracted and fish are caught and eaten. On this occassion waste from the process was being dumped into a local river, which had already caused local villages to stop using it as a sourse of drinking water. Local authiorities are extremely concerned about the potential impact of this on settlements further downstream, including the city of Jambi, which has a population of about 600 000.

Sumatra has a wet tropical climate, with a rainy season that lasts from October to April, when rainfall typically reaches 200-300 mm per month and a dry season from May to September, when rainfall is usually below 200 mm per month (though the area is never truly dry. This is driven by the Southeast Asian Monsoon Seasons, with the Northeast Monsoon driven by winds from  the South China Sea fuelling the wetter rainy season and the Southwest Monsoon driven by winds from the southern Indian Ocean the drier dry season. Such a double Monsoon Season is common close to the equator, where the Sun is highest overhead around the equinoxes and lowest on the horizons around the solstices, making the solstices the coolest part of the year and the equinoxes the hottest.

The winds that drive the Northeast and Southwest Monsoons in Southeast Asia. Mynewshub.

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Tobleria bicuspis: The earliest cone-producing Conifer?

Modern Conifers bear their seeds in cones, structure in which the seeds are attached to scales arranged spirally on a central bract. A similar situation is seen in Conifers from Mesozoic and Cainozoic deposits, but the earliest, Carboniferous Conifers, placed in a group called the Voltziales, are somewhat different, with seeds found in the axils of fertile leaf shoots (the angle between the base of the leaf shoot and the stem), which are arranged in a loosely radial pattern on a stem. The first seed cones appear in the Voltziales towards the end of the Early Permian.

In a paper published in the journal PhytoKeys on 25 March 2019, Isabel Van Waveren of the Naturalis Biodiversity Center discusses the peasence of cones in Tobleria bicuspis, a Voltziales Conifer from the Earliest Permian Jambi Palaeoflora of Jambi Province in Sumatra, Indonesia.

The Jambi Palaeoflora comprises a number of coalified plant fossils excavated from outcrops of the Mengkarang Formation along tributaries of the Merangin River. These deposits are thought to be between 296.77 and 296.14 million years old, and were laid down in a tropical forest about 15° north of the Equator. Eighteen samples were used in the study, seventeen of which were collected in 1925 by Wilhelmus Jongmans and Walther Gothan, plus one specimen collected from the same area in 2006.

Map of the Bangko area showing the outcrops of the Mengkarang Formation along the distributaries of the Merangin River where Tobleria bicuspis was found. Van Waveren (2019).

Examination of the samples found that they had cones made up of tightly packed bicuspid (double tipped) scales (typical for cone-bearing members of the Voltziales). The most intact of these (from sample 45311, a slab of light beige, finely banded, tuffaceous mud collected along the Karing River by Jongmans and Gothan) is 24 mm long, and 8-9 mm wide at the base, tapering to about 4-5 mm, although this is not a complete cone, with the base being broken so that it would have originally been somewhat longer.

The three cones from sample 45311: (A) cone C1, (B) Tobleria bicuspis right edge of cone C2 fragment showing bicuspid scale and seeds (C) Tobleria bicuspis cone C3 fragment showing bicuspid scale. Arrows 1–4 in Figure (A) indicate scales in side view, arrow 5 indicates the cone axis. The arrow in Figure (C) indicates a bifid scale. Scale bars: 10 mm (A); 2,5 mm (B); 5 mm (C). Van Waveren (2019).

Each of the scales is about 3 mm wide and 5 mm long, and has two, linked 'fertile utits' (seeds) on its inner surface. These 'fertile units' vary somewhat in shape, from adpressed hemispheres, to heart-shapes attached at the central and narrowest points, to paired almond shapes. These vary in length between 0.6 and 2.6 mm, and in width between 0.4 and 1.6 mm.

Details of dispersed seeds, scales and fertile scales: (A) paired seeds with double wall (sample 45311C) (B) paired seeds with triangular micropylar protrusion (sample 45311 E) (C) detail of triangular micropylar protrusion from paired seeds (sample 45311 E) (D) heart shaped paired seeds/ovules (sample 45311 D) (E) heart shaped paired seeds/ovules (sample 45311 B) (F) juxtaposed almond shaped seeds/ovules (sample 45311 B) (G) bicuspid scale (sample 45311 Aa) (H) bicuspid scale (sample 45311D) (I) bicuspid scale (sample 45471) (J) bicuspid scale with contour of two seeds/ovules (sample 45315) (K) bicuspid scale with darker organic contour of seed (sample 45310) (L) bicuspid scale with heart shaped contour of seeds/ovules (sample 45471). Van Waveren (2019).

Van Waveren notes that four Conifer groups were producing cones by the end of the Permian, the Cordaitanthales, the Ferugliocladales, the Dicranophyllales, and the Voltziales, as well as three non-Conifer groups, the Cycadalean, the Gnetaleans, and the Peltaspermaleans. The first Cycad cones appear in the Early Permian, but are quite distinct from Conifer cones, with their seeds located laterally to (sideways of) their cones, the earliest known Gnetalean cones appear in the Late Permian of China, and are spear-shapes, with single seeds, and the Peltaspermaleans have very rounded scales. The scales and seeds of the Cordaitanthaleans form a distinct wing shape, while the seeds of the Ferugliocladales are attached to the cone axis rather than the scales, while the scales of the Cheirolepidiales are triple in form, but encase a single seed. The cone-bearing Voltziales, in contrast typically have bicuspid cone-scales and double seeds, leading Van Waveren to conclude that the placement of Tobleria bicuspis in this group is quite safe taxonomicaly.

Reconstruction of Tobleria bicuspis. Scale bar is 1 cm. Van Waveren (2019).

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Eruption in Mount Karinici, Indonesia.

The Darwin Volcanic Ash Advisory Centre has reported an eruption on Mount Karinici, Sumatra, that produced an ash column 4.3 km high on Sunday 13 August 2017. This column persisted for several days, having drifted only 30 km to the southwest by Thursday 17 August. Mount Karinici, which is located in the Karinici Sablat National Park, on the border between West Sumatra and Jambi Provinces, is the highest volcano in both Sumatra and Indonesia, and one of the most active, typically undergoing several eruptions in the course of a year. However most of these eruptions are quite small; the volcano is not considered to be particularly dangerous, and is a popular tourist attraction.

The location of Mount Karinici, Sumatra. Google Maps.

The Indo-Australian Plate, which underlies the Indian Ocean to the west of Sumatra, is being subducted beneath the Sunda Plate, a breakaway part of the Eurasian Plate which underlies Sumatra and neighbouring Java, along the Sunda Trench, passing under Sumatra, where friction between the two plates can cause Earthquakes. As the Indo-Australian Plate sinks further into the Earth it is partially melted and some of the melted material rises through the overlying Sunda Plate as magma, fuelling the volcanoes of Sumatra.

The Subduction zone beneath Sumatra. NASA/Earth Observatory.

The two plates are not directly impacting one-another, as occurs in the subduction zones along the western margins of North and South America, but at a steeply oblique angle. This means that as well as the subduction of the Indo-Australian plate beneath the Sunda, the two plates are also moving past one-another. This causes rifting within the plates, as parts of each plate become stuck to the other, and are dragged along in the opposing plate's direction. The most obvious example of this is the Sumatran Fault, which runs the length of Sumatra, with the two halves of the island moving independently of one-another. This fault is the cause of most of the quakes on the island, and most of the island's volcanoes lie on it.

The movement of the tectonic plates around Sumatra. NASA/Earth Observatory.

 

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Three killed by Sumatra landslide.

Three people have reportedly been killed and another three seriously injured following a landslide at the  village of Tambang Tinggi in the Sorolangun District of Jambi Province on Sumatra, on the evening of Thursday 26 February 2015. The three deceased have been named as Mariam, Desi and Tanto, while the injured have been named as Inam, Zainab and Raimah. The incident took place following sustained heavy rains in the area; landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall. 

The approximate location of the 26 February 2015 Tambang Tinggi landslide. Google Maps.

Jambi Province has a  wet tropical climate, with 2000-300 mm of rain per year and a wet season that lasts from October to March, with peak rainfall in January. Landslides are a common problem, particularly as a rising population is leading both to increasing deforestation (which removes tree roots that can stabilize slopes) and more people settling on or close to slopes where they are vulnerable.

The Tambang Tingii landslide has been linked by the Jambi Provincial Police to illegal mining in the area. Unlicensed artisanal mining is common on Sumatra, where many areas have deposits of alluvial gold (gold which has been eroded out of rocks elsewhere and deposited by rivers in places where the river slows - often at higher concentrations than it would have been found at in the original ore-rocks). The practice has widely been linked to increased erosion, flooding and landslide events, partly because of the associated deforestation (removal of trees which help stabilize soil in order to get at underlying deposits) and also because many miners excavate into river banks, where the highest concentrations of gold are found, leading to weakened banks and often changing the course of rivers. Attempts by local authorities to clamp down on such activities are often hampered by a perception that restrictions favour foreign mining companies, which do not always have a good reputation for environmental management or their treatment of local people.

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