Four people have been confirmed dead and three more are missing following a landslide on the island of Guadalcanal in the Solomons on Thursday 12 March 2020. The event happened at Lambi on the west coast of the island amid heavy rains and flooding associated with a low-pressure system that swept across the islands. 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 12 March 2020 Guadalcanal landslide. Google Maps.
The Solomon Islands has a tropical climate, with a wet season that runs
from November to April and a dry season that lasts from May to October.
However, the dry season is not completely arid, typically still receiving
about 100 mm of rain per month, and this year has been exceptionally
wet, with some of the heaviest rain ever recorded in the islands falling
in the past week, and local authorities are warning there is a danger
of further landslips and flooding.
Damage to Takaboru Bridge on Guadalcanal Island following days of heavy rain in the area. Loni Sitana/Facebook.
Low presure systems 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 inrushing 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 weather systems 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.
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