Three people have died in two separate landslides after Hurricane Eta made landfall in Nicaragua on Tuesday 3 November 2020. Two miners were killed at a gold mine in Nicaragua, while a thirteen-year-old-girl was killed in another event at San Pedro Sula in northern Honduras. 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 storm was a Category 4 Hurricane when it made landfall, bringing with it winds of up to 225 km per hour, to the south of the city of Puerto Cabezas. It has lost energy as it has passed over Central America, and been downgraded from a hurricane to a tropical storm, but it is expected to travel northwest over the next few days, gaining strength again as it passes over the Caribbean, and potentially threatening the populations of Cuba and Florida. The casualty rate was probably been kept down by the evacuation of about 20 000 people from its path in Nicaragua, though it has caused widespread flooding and left about 60 000 people without electricity supplies in and around Puerto Cabezas.
Storm damage in Puerto Cabezas, Nicaragua, following the passage of Hurrican Eta. CNN. 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 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
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
path and strength of Hurrican Eta. Thick line indicates the
past path of the storm (till 9.00 am GMT on Thursday 5 August 2020),
while the thin line indicates the predicted future path of the storm,
and the dotted circles the margin of error 21, 33, 45, 69, 93 and 117 hours
ahead. Colour indicated the severity of the storm. Tropical Storm Risk.
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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