After the devastating earthquakes in the oceans off American Samoa and Indonesia this week, seismologists say more is to come from the Pacific ‘Ring of Fire’, the most active quake and volcano zone on the planet.
Of the approximately 1,5-million earthquakes that occur around the world every year, only one on average is a more-than-eight-magnitude monster. But five of the eight quakes of this size that have shook the earth since the enormous 9.3-magnitude Boxing Day event in 2004 have been inside the Ring of Fire.
The zone, which extends from Japan down to the Philippines and Indonesia – and in the Americas, from Alaska to Chile – is home to about 90 per cent of the world’s earthquakes. More than half of the world’s active volcanoes above sea level are also part of the ring.
The theory of plate tectonics, which was developed by scientists in the 1960s, explains the region’s awesome destructive power.
According to the theory, the earth’s crust is made up of a quilt of massive plates, about 80 kilometres thick, which float above the planet’s hot, molten interior. For eons, around 70 of these plates, some of which are larger than a continent, have been moving past each other at the rate of a few centimetres per year. Energy builds up at the plates’ fault lines: when the energy is suddenly released, earthquakes occur.
The volcanic islands of the Indonesian archipelago closely follow the border between the earth’s most active tectonic plates. Amongst the newest real estate on the planet – the island chain was formed some 15-million years ago – Indonesia owes its shape to the same seismic forces that produce earthquakes. The country’s 155 centres of active volcanic activity, which mark its location along the fault line, bear testament to its violent birth and recent history, as well as to its likely future.
Famously, the eruption of Indonesia’s Mount Tamborra in 1815 came with few warning signs. Five days before the event, explosions were heard almost 1,500 kilometres away, but were taken to be cannon fire. The ‘super-colossal’ blast – at a volcanic explosivity index (VEI) of seven – released flames 40 kilometres into the air, and the enormous rock and sulphur-dioxide emissions resulted in 1816 being remembered, worldwide, as the ‘year without summer’. The final death toll was over 70,000.
Perhaps even more famously, the Indonesian island of Krakatoa was almost entirely destroyed by a series of gigantic explosions in 1883, which were heard nearly 5,000 kilometres away. The combined effect of pyroclastic flows, volcanic ash and deadly tsunamis ‘officially’ killed 36,000 people, although some estimates place the tally at closer to 120,000.
But it was 2004’s Boxing Day tsunami, the result of an earthquake off the island of Sumatra, that claimed the most lives in Indonesia’s long history of natural disasters – 240,000 dead across Asia, with 170,000 fatalities in Indonesia alone.
The 9.3-magnitude 2004 quake, according to seismologists, has modified some of the stresses and pressures in the ‘Ring of Fire’ region, and is more than likely responsible for the increase in seismic activity over the past five years.
Many seismologists agree that this week’s 7.6-magnitude quake off Sumatra – which claimed 500 lives (and counting) in the city of Padang – can be directly linked to the Boxing Day disaster. A few seismologists go further: the region is building up to another event of truly cataclysmic proportions, they say.
By: Kevin Bloom