Beat The BearBeat The BearPeople who live in areas of high seismic activity are well aware of the devastating power that can be unleashed by earthquakes and volcanoes. Areas which are regularly affected tend to have plans for evacuation and support for the inhabitants although it is hard even in prepared regions to be ready for every eventuality. The nature of these forces is that they are unpredictable in timing and extent.
Earthquakes do not necessarily limit their destructive force to the immediate vicinity of the epicentre. Devastating tsunamis are not merely distant folk memories remote in time or limited to far-off and exotic lands. The Sumatra-Andaman earthquake of 2004 is estimated to have killed 230,000 people either directly or through the resulting tsunami[1] - the effects of tsunamis being highly variable but able to travel thousands of miles/kilometres from the epicentre of the quake. In 2011 an earthquake off the coast of Japan caused a tsunami which had very serious effects on the Japanese coastline and rendered the Fukushima nuclear plant inoperable, the death toll being estimated at around 16,000 and a further 230,000 people displaced, some permanently[2].
In case anyone should be complacent about the tsunami risk in their own region, it's worth noting that the UK is in one of the least seismically active areas of the planet, yet in 1607 a tsunami is though to have devastated the region around the Bristol channel[3], the 1755 Lisbon earthquake tsunami caused damage as far away as Galway and Lagos[4] and there is speculation that an asteroid strike may have caused a large tsunami which struck the south of England in 1014[5]. Wikipedia has a list of supected tsunamis to affect the British Isles[6].
Earthquakes and tsunamis tend to be events of short duration but with long lasting effects due to the damage caused to infrastructure and the number of deaths associated with them. A longer-term and more severe threat is associated with volcanoes.
It's speculated that the eruption of Mount Toba initiated an ice age and eliminated most human life on the planet some 70,000 years ago[7]. Whilst that might sound like prehistoric times, geologically speaking it's recent. In more modern times the eruptions of Tambora[8] and Krakatoa[9] in the 19th century are both thought to have cooled the entire planet enough to seriously affect agricultural production (here Tambora is believed to be at least partly responsible):
"In Europe and Great Britain, far more than the usual amount of rain fell in the summer of 1816. It rained nonstop in Ireland for eight weeks. The potato crop failed. Famine ensued. The widespread failure of corn and wheat crops in Europe and Great Britain led to what historian John D. Post has called "the last great subsistence crisis in the western world." After hunger came disease. Typhus broke out in Ireland late in 1816, killing thousands, and over the next couple of years spread through the British Isles."
In 1991 Mt Pinatubo erupted and, whilst much smaller in effect than the 19th century events, led to noticeable global cooling[10]. In 2010 the eruption of Eyjafjallajökull in Iceland caused an ash plume which shut down aviation in Northern Europe for several days[11], whilst informed sources appear to expect that Katla in Iceland is liable at some point to erupt with consquences very much larger than Eyjafjallajökul[12].