For as long as I can remember 'Lituya Bay' has been lodged in my deep subconscious. I don't know where I picked it up, probably as a kid whilst reading the Readers Digest Bumper Book of Essential Knowledge on a bored, rainy day...
Lituya Bay, somewhere in deepest Alaska, the scene of the world’s biggest recorded wave. As a junior surfer this annoyed me. You see it wasn't a proper wave, not a mighty ocean swell from an explosively cyclogenic 'perfect' storm, not even a tsunami, the ungodly offspring produced by tectonic plates coupling. It was a con, a hoax, a one in a million shot, an aberration of nature. Originally it was also misunderstood. American geologists first noticed something strange at Lituya during the early fifties whilst surveying for oil. Normally the primordial forest reaches right down to the shoreline but in the bay they found an unusual demarcation. At about one hundred and fifty metres above sea level the mature growth ceased and below it much younger trees sprouted.
It was as if some unknown force had just wiped the slate clean and nature started afresh. The geologists were stumped.
In an early attempt at scientific cross-pollination they took samples from trees around the trim line and had the tree ring section analysed. The results were conclusive, a powerful force had surged into that forest leaving the surviving mature trees on the edge of the tree line badly bruised. The only feasible explanation was that a wave had hit the forest up to a height of one hundred and fifty metres above sea level… This was completely outside the box, a wave the height of a fifty-storey building?
The most recent and well-known tsunami had hit Hilo, in Hawaii, in 1946, causing mass devastation and killing a hundred people. It came from a sea floor quake thousands of kilometres away and whilst being phenomenally destructive the wave was only ten-metres high. The geologists knew that normal earthquake-generated tsunamis are inherently limited in size by the disturbance that caused them. Meaning a ten-metre displacement of the sea floor results approximately in a ten metre high wave on the surface.
The geologists left Lituya Bay in 1953, completely mystified, having found no oil and no explanation for what they had seen. It was a mere five years before they got their answer. Another huge wave hit Lituya Bay; this time there were witnesses.
July 9th, 1958. Three fishing vessels are moored in the calm haven of Lituya, at around ten o'clock in the evening the tranquillity is broken by an unearthly rumbling coming from the mountains at the head of the bay. A minute later a monstrous wall of water is bearing down on the boats. Paralysed with fear the crew of one boat watches as forty fathoms of anchor chain pay out before snapping like a cheap piece of string. Amazingly that one boat surfs the wave over the treetops and comes back to rest in the bay, the other two craft are washed out to sea and smashed into kindling. One two-man crew dies the others somehow survive...
Dawn revealed a scene of total devastation. Trees and soil stripped away leaving bare bedrock up to five hundred and twenty metres above sea level. Surveying by plane the next day one of the original geologists spotted something different at the head of the bay. On closer inspection it became apparent that a massive section of mountain had fallen off, into the bay. This time it was obvious what had happened. A massive cataclysmic landslide. It soon became apparent that the Lituya wave was indirectly caused by a strong earthquake after all, it was the quake that had induced the rock fall. It is a commonly known fact that throwing a stone into a pool of water makes ripples. Drop ninety million tonnes of rock into a pool of water and the same effect is observed. The ripple that results is, however, higher than any skyscraper yet built. This got the scientists of the world thinking. Why did this happen? Could it happen anywhere else? What would happen if this occurred in a populated area? Answers to the first two questions came quickly, the latter we are yet to discover.
Abundant sea floor surveys in the sixties showed that this was a common occurrence around one particular kind of location - the large volcanic island. Of which, as surfers, we know plenty; Hawaii, Reunion, Madeira, the Azores, the Canaries, and the list goes on. As these islands grew (or, in the case of Hawaii's Big Island, grow) by successive eruptions of lava and volcanic rubble, they build an inherently unstable structure and are prone to periodic collapse. Anyone who has been to Madeira and wondered why the village of Jardim do Mar sits on a relatively flat coastal platform when the bulk of the island is surrounded by steep cliff, here’s your answer: It’s the top of a massive landslide; the scoop shape in the cliffs above the village show where the material came from.
When the scientists started looking they found evidence for past collapses everywhere.
In Hawaii the seafloor is littered with massive chunks of rock that have fallen in the past. The largest is the Tuscaloosa seamount, a giant block so big it is nearly ten-times the volume of Mt Everest; it fell off Oahu two million years ago. Eighty thousand years ago Cape Verde suffered a massive collapse and most recently Reunion Island in the Indian Ocean lost some volume, a mere four thousand years ago. All these events would have generated huge waves, now known as mega-tsunamis. These waves would have hit the West Coast of America, North Africa and West Australia respectively. It’s happened in the past but can it happen again?
Current opinion is “It's not a question of if, it's a question of when”. Prime contender is the Canary Island of La Palma; the southern end of the island is home to the active volcano known as the Cumbre Vieja. The flank of the volcano slipped seawards during the last eruption there in 1949 opening a two-kilometre fissure along the ridge. A chunk possibly twenty kilometres long and weighing roughly half a trillion tonnes is poised to fall. The mechanism by which this may happen is the source of much debate, but the volcano is still active and, due to unusual geological conditions, is full of water. If magma starts to rise again all the ingredients are there for a massive rock fall and accompanying mega-tsunami. So consider it, if you will, as a loaded gun. Primed, cocked and aimed at the plump target of the East coast of the United States. If the predicted collapse occurs the mega-tsunami would bring ruination to New York, Boston, Miami and the Caribbean not to mention twenty kilometres inland.
There is evidence of a collapse on an island near La Palma from around one hundred and twenty thousand years ago. This is proposed by some to have been responsible for a wave, which has had a lasting impact on the coast of the Bahamas. The thousand tonne chunks of sea floor rock, which now rest high above sea level, are enticing proof.
The problem with mega-tsunamis is the huge wavelength; normal storm generated waves as seen in spectacularly large style at Mavericks, Jaws et al have a wavelength in the order of a few tens of metres. Mega-tsunamis have a wavelength of kilometres. When they approach land they don't just break, they engulf. (Think of the special effects in the movie Deep Impact: it's accepted that there are many similarities between asteroid and rock fall generated waves and the Boxing Day tsunami gives a vivid insight into the process). The huge wall of water at the leading edge of the wave doesn't just break on the coast the whole wave surges many miles inland.
Is this just hyperbole? Well, large volcanic islands have frequently suffered massive collapses (frequent on a geologic time scale anyhow), and will continue to do so. The Cumbre Vieja may collapse next year, it may collapse next millennium, but it will collapse. And as long as it does so in the predicted spectacular fashion the Lituya Bay event will lose its title to the world’s biggest wave.
It is, however, unlikely at this time that Readers Digest are holding the press on the new revised edition of the Bumper Book of Essential Knowledge…
