Ta'u is the easternmost island in the Samoan chain that has outcropping of basalt that
actually relates to the Samoan hotspot.
There is evidence that a large landslide occurred in the south side of Ta’u.
If you look at the shape the morphology of Ta’u island you’ll see that on the north
slope of the island is a relatively shallow slope.
By contrast, the south side of the island you have this near vertical wall and this
vertical wall is more than a thousand feet high.
You have this incredible sense that a lot of mass is missing and our reason for believing
that is that preliminary sonar imagery of the ocean floor shows inexplicably large blocks
almost like a debris field thats directly beneath and to the south of the south side
of Ta'u. Flank failure on the south side of Ta'u would be devastating for the region.
The greatest energy would be focused to the south so the largest tsunamis would be generated
due south of Samoa, but the energy travels radially.
The waves traveling to the west would be expected to be hundreds of meters high, certainly by
the time they encounter Ofu and maybe many tens of meters high by the time they encounter
Tutuila and Upolu.
But there is no real modern example for this in modern human history.
The mechanism that is responsible for generating most of the tsunamis in the Samoan region
would be the large scale mega thrust earthquakes that occur just to the south of us along the
Tonga Trench.
We have an example from two thousand nine.
It was my first time in my life I had ever personally witnessed the devastation of a
tsunami.
It's always hard to guess the future.
But the Samoans are almost certainly going to experience more large tsunamis in the future.
Just because these islands are situated near a seduction zone thats generates the highest
frequency of large mega earthquakes on earth.
So they are always going to face that issue.
The question is what other potential hazards do they face in the region.
What what other mechanisms exist for generating large tsunamis in the region and the potential
certainly exists for flank failures on some of the islands Ta'u and possibly Savai'i to
generate tsunamis in the future.
We have some evidence we need more evidence of course that tsunamis may have been generated
by flank failure of Ta'u in the past.
This cruise will provide us with the potential to evaluate whether or not submarine landslides
have caused tsunamis in the past.
We really don't have good maps of the debris fields located to the south of Ta'u.
Those are really needed.
These are really the missing link in this whole hypothesis that the south side of Ta'u
is missing a big chunk of land as the result of flank failure in the volcano.
So what we need to do is look for the missing pieces.
If it's the result of flank failure, you've got see the rubble to the south of Ta'u.
We need better maps to see if the rubble is there.