This is embarassingly late, but then, I've had houseguests. Please forgive the lack of immediacy. Some days ago, I pointed out the work of Australian geologist Edward Bryant. He's the guy who maintains that Australia has been hit by some truly monstrous tsunamis in the past, perhaps even as recently as five hundred years ago.

I thought it would be helpful to expand upon some of his observations. For starters, some practical advice on survival.

Not all coastlines are exposed to tsunami. On the open coast, beaches, headlands, and cliffs are unsafe. Beaches are swamped while headlands that jut out onto the shelf receive the full force of any tsunami. Cliffs—even 100 m ones—also pose no barrier to a tsunami, because their height is puny compared to the 100 km wavelength of the tsunami. The back corner of an embayment is the safest place to flee to if a tsunami approaches one of our beaches.

Islands are also dangerous. They tend to sit further out on the continental shelf. More important, tsunami will wrap around islands and become higher on the lee side. Here, the centre of the island is the safest place to seek refuge.

If one is on a boat, one should never come into shore, shelter behind a headland, or enter a harbour following a tsunami warning. Tsunami increase dramatically in height in water depths shallower than 20 m depth. They also increase in size inside harbours where resonance can operate. Rivers leading from bays are also vulnerable...

Coastal floodplains within a few meters of sea level are also at risk. Once a tsunami gets onto a floodplain, it moves inland—depending on the type of obstructions—as if it was moving through shallow water. A ten-metre high wave could conceivably travel 8-10 km inland on a delta covered in pasture.

On a forested delta, the same wave would only penetrate 500 m inland. The fifteen-metre high tsunami in Papua New Guinea in 1998 never travelled more than 600 m inland through trees. If houses cover the floodplain, the same sized wave would only travel a few hundred meters.

However, all buildings, including those made of reinforced concrete, would be destroyed. If the wave were only 3-4 m high, all buildings except wooden ones could survive... in an urban coastal area if you were standing on a beach such as Bondi.... You could simply turn and run to the nearest multi-storied building, making certain that it was not a block of flats with a secure entrance.

You would then take the elevator to the top floor or run up the stairs one-to-two floors. Not only would you be positioned above flood level for most tsunami, but the building would also escape destruction.

These safety points are universal. They are worth remembering on your next holiday to any shoreline whether it is Waikiki Beach, Hawaii, the windswept coast of Northern Scotland, or the banks of Warragamba Dam. A tsunami will happen again, sometime soon, on a shoreline near you—on a reservoir, a lake, a sheltered sea, inside a coral barrier reef, in the lee of an island or along an open coast.

That was excerpted from Dr. Bryant's website. In his book, he considers the merits of climbing a tree. They are considerable, especially if you have run out of other options. If you examine the area of a tsunami incursion you will find that many (though not all) trees in the area stay rooted far more effectively than a wood frame structure, even one that is bolted to its foundation. It may be a slim hope, but if you can't outrun the wave, the right tree might save your life.

Here's an interesting picture from Dr. Bryant's files. It depicts a minivan sized boulder perched on the edge of a seaside cliff. If you were like me, strolling along on a sunny afternoon, it might not occur to you to wonder where that boulder came from. There is nowhere it could have dropped or rolled from.

Glaciers didn't carry it. Most likely it was washed up from below. The cliff in question is over one hundred feet high. Here are a few more boulders, a bit less than fifty feet above sea level. Some practical advice we might infer is that one should NOT stand on a cliff edge to view an incoming tidal wave "in safety".

More to follow as time and guests allow.