Geoscience Reference
In-Depth Information
There is another problem. If significant parts of the Greenland and Antarctic ice sheets
melt, the removal of ice from the continent means that it will recover and start to move
upwards. This isostatic rebound can be seen in the British Isles, which are still recovering
from the last ice age, with Scotland still rising while England is sinking. This will mean
that the relative sea level around the continental shelf will fall, removing the weight and
thus the pressure of the seawater on the marine sediment. Pressure removal is a much
more efficient way of destabilizing gas hydrates than temperature increases, and so huge
amounts of methane could be released from around the Arctic and Antarctic.
There is another secondary effect of gas hydrate release: when the hydrates break down,
they can do so explosively. There is clear evidence from the past that violent gas hydrate
releases have caused massive slumping of the continental shelf and associated tsunamis
(giant waves). Eight thousand years ago the Norwegian Storegga slide, which was the size
of Wales, produced a 15 m high tsunami that wiped out many prehistoric settlements in
Scotland. In modern times, we have seen the destruction caused by the 2004 Boxing Day
Indian Ocean and the 2011 Japanese tsunamis. Hence we cannot rule out the possibility
that climate change could lead to an increased frequency of gas hydrate generated submar-
ine landslides, and thus tsunamis of over 15 m in height hitting our coasts. Up to now,
only the countries around the Pacific rim are prepared for this type of tsunami event—but
gas hydrate generated tsunamis could occur anywhere in the ocean.
