Geography Reference
In-Depth Information
diameter created a massive fireball that exploded some 8 km above the earth. Its blast
was heard 1000 km away, people and animals at half the distance were knocked off
their feet, and a 1000 km
2
area of forest in Tunguska, Siberia in 1908 was destroyed,
luckily an uninhabited forested area. Similar sized occurrences have been estimated
to occur once every 300 years, but with only ten times that incidence probability of
hitting populated areas (Abbot and Sampson
2009
, p. 485). The Chelyabinsk meteor
that fell in southern Urals on 15 February 2013 was the largest recorded since the
Tunguska example. It has been estimated to have been originally 19 m in diameter
and over a million kg. (12,000 t) in weight and entered the earth's atmosphere at
67,000 km/h creating a huge fireball. However more than three-quarters burned
up during its decent which climaxed in a big explosion which released half a mil-
lion kilotons equivalent of TNT, 20-30 times the size of Hiroshima's atomic bomb,
so that the largest fragment found was only 635 kg. The huge shock wave caused
damage to 7200 buildings, mainly window and balcony damage, with 1500 people
seeking medical attention mainly from cuts caused by the flying glass. One teacher
who saw the fireball told her students to duck and hide under desks which saved
them, although she was injured. Fortunately the area affected was relatively sparsely
populated and no settlements were at the impact site (Popova et al
2013
).
However, a large meteor may not just affect one place, but life in general. For
example, there is now general agreement that it was large asteroid impact on what
is now Yucatan some 65 million years ago, in combination with a series of volcanic
eruptions, that led to a mass extinction that wiped out the dominant dinosaurs, and
heralded the end of the period we call the Cretaceous. This was not because of the
direct local or regional effect, but through the resultant cloud of dust that cloaked
the earth for years, reflecting solar radiation back, which created colder tempera-
tures and the loss of vegetation, followed by much warmer temperatures when the
dust settled and the greenhouse gases generated remained in the atmosphere. Debate
continues about whether governments should co-operate in devising measures to
combat such large scale hazards. The only real progress so far has been the willing-
ness of the U.S.A. in 1998 to fund an asteroid tracking programme, and 10 years
later we know the presence and orbits of some 6 thousand large asteroids, of which
almost a sixth have been classified as hazardous if they hit the earth. However
extra-terrestrial impacts do not only come from space rocks. There have also been
recurring episodes of large solar flares, such as the largest one recorded to date in
early September 1859 (Boteler
2002
; Lovett
2011
). It produced spectacular auroras
in most parts of the world, but more seriously it disrupted the nascent telegraph sys-
tem, causing electrical shocks to operators and destroying many pylons. It has been
suggested that a similar solar storm today would disrupt radio communication be-
cause of the flare's high energy output of X rays, while the slower travelling coronal
mass ejection of charged particles would interact some 3 days later with the earth's
magnetic field. This would create power surges in electrical grids, destroying many
transformers and cutting out power to cities for weeks, if not months, as well as
destroying GIS and satellite connections. Prediction of such space events is in its
infancy, but it has been suggested that solar storms of this magnitude only occur ev-
ery 500 years. Nevertheless, these events may be some of the most severe threats to
