Seven dead and four missing in two landslides on Luzon Island, the Philippines.

Seven people have died and four more are missing following a series of landslides on southern Luzon Island in the Philippines on Friday 28 and Saturday 29 December 2018. The first event happened in the city of Legazpi in Albay Province, late on Friday, and resulted in the deaths of Mauro Alegre, 25, his wife Mia, 20, and their son Marco, 3, when a landslip destroyed their house; a further ten people were injured in the event. A further two incidents happened the next day, the first at bout 2.00 am local time, in the town of Lagonoy in Camarines Sur, when part of a hillslope collapsed onto a house, killing Charles Las Penas, 51, and his son, also Charles, 11. In a third incident a landslide in the village of Osiao in Sorsogon Province is known to have killed two people, Gilbert Desunia and Gerald Despabiladeras, with four more missing, Dominador Esquivel, Leonel Diaz, Magno Diaz, and Franklin Olavere, and another four requiring hospital treatment, Mark Diolata, John Carlo Lorill, John Robert Marcaida, and Arjay Dulpina.

The aftermath of a landslide in Legazpi City in Albay Province, the Philippines, on Friday 28 December 2018, which killed three people and injured ten more. Luence Burce Barcena/CNN Philippines.

The landslips occurred as southern Luzon was battered by rains associated with the passage of Tropical Depression Usman across the island. 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 path and strength of Tropical Depression Usman. Thick line indicates the past path of the storm (till 6.00 pm GMT on Saturday 29 December 2018), while the thin line indicates the predicted future path of the storm, and the dotted circles the margin of error at 12, 24, 36, 72, 96 and 120 hours ahead. Colour indicated the severity of the storm. Tropical Storm Risk.

Tropical depressions are caused by the warming effect of the Sun over tropical seas. As the air warms it expands, causing a drop in air pressure, and rises, causing air from outside the area to rush in to replace it. If this happens over a sufficiently wide area then the inrushing winds will be affected by centrifugal forces caused by the Earth's rotation (the Coriolis effect). This means that winds will be deflected clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere, eventually creating a large, rotating Tropical Storm.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

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Spilosmylus spilopteryx & Spilosmylus tephrodestigma: Two new species of Osmylid Lacewing from Luzon Island, the Philippines.

Osmylids (Osmylidae) are a group of Neuropteran Insects with a fossil record dating back to the Early Jurassic, with a stem group lineage (i.e. fossils of species more closely related to them than to anything else, but not descended from the last common ancestor of all living species), that are still in existence today. They appear to have been at their most numerous and diverse in the Middle-Late Jurassic, with a number of lineages apparently disappearing at the Jurassic-Cretaceous boundary.Living Osmylids tend to be large, and often have strongly patterned wings. Their larvae have elongated, lance-like mandibles, giving the group the alternative name 'Lance Lacewings'.

In a paper published in the journal ZooKeys on 26 October 2017, Davide Badano of the Dipartimento di Scienze della Terra at the Università degli Studi di Genova, and Shaun Winterton of the California State Collection of Arthropods, describe two new species of Osmylids from Luzon Island in the Philippines. Both are placed in the genus Spilosmylus, which is found from East Africa across South and Southeast Asia and as far east as Australia. 

The first new species is named Spilosmylus spilopteryx, where 'spilopteryx' means 'marked wing' in reference to the prominent, cloud-like markings in its wings. It is described from a single male specimen collected from the Tigaon area of Camarines Sur Province on southern Luzon. It is 10.48 mm in length, with a forewing length of 17.46 mm, and brown in colour with distinctively marked wings.

Spilosmylus spilopteryx, male specimen in dorsal view. Badano & Winterton (2017).

The second new species is named Spilosmylus tephrodestigma, where 'tephrodestigma' means 'coal spot' in reference to the grey spots found on its forewings. This species is described from a single specimen from the Barlig area of Mountain Province on northern Luzon Island. This specimen has a damaged abdomen, making it impossible to determine its sex or body length, but it has a forewing length of 21.43 mm, and is pale in colour with brown markings on its body and grey markings on its wings.

Spilosmylus tephrodestigma, specimen in dorsal view. Badano & Winterton (2017).

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Landslide kills man in Camarines Sur Province on Luzin Island in the Philippines.

A man has died after the house he was in was crushed by a landslide in the village of Sibaguan in Camarines Sur Province on Luzon Island in the Philippines on Thursday 2 November 2017. The incident happened slightly before 1.00 pm local time, following several hours of heavy rain. 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 man has been identified as Ryan Lasmariñas, 32. A second man who was in the house escaped unharmed.

 

The scene of a landslide that killed a man in Camarines Sur Province, the Philippines, on 2 November 2017. GMA News.

The rains which triggered the landslide are associated with Tropical Depression Ramil, a storm system which has passed over the Philippines this week, bringing heavy rains to Luzon and neighbouring islands.

 The passage of Tropical Depression Ramil till 8.00 pm local time on 2 November 2017, grey area to the left is the projected future track of the storm. Philippine Atmospheric Geophysical and Astronomical Services Administration.

A Tropical Depression is a Tropical Storm not powerful enough to be formally named (though they are often given names locally). Tropical storms are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the in rushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere.These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.

The low pressure above tropical storms causes water to rise there by ~1 cm for every millibar drop in pressure, leading to a storm surge that can overwhelm low-lying coastal areas, while at the same time the heat leads to high levels of evaporation from the sea - and subsequently high levels of rainfall. This can cause additional flooding on land, as well as landslides, which are are a common problem during these storms.

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