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PACIFIC SCIENCE, VoL XXII, October 1968 
The northeast rift zone of Ta’u, along which 
the Luatele shield, Lualaitiiti pit crater, and at 
least two vents at Fitiiuta are perfectly aligned 
(Fig. 2), extends to more than 5,000 feet below 
sea level. Four or five extra-caldera cones are 
also aligned along a radial rift just to the south, 
but there is no indication of a submarine ridge 
continuing offshore. 
Geomorphology 
STREAMS AND valleys: The radial drainage 
pattern of the original Lata shield is still present 
today, although somewhat modified by faulting 
and later volcanism. Faleiulu Stream, for ex- 
ample, is a radial stream on the Lata shield, but 
where it encounters Tunoa shield, it is deflected 
to the north. Daly’s statement (1924:132), 
"The deepest gorge observed is about 5 meters 
in depth," is correct for most of the island. 
However, along the northern coast, Avatele, 
Matautu’ao, and ’Ao’auli streams have cut deep 
valleys into pre-caldera flows where apparently 
no later post-caldera volcanism occurred. ’Ao’auli 
and Matautu’ao streams have cut canyons more 
than 300 feet deep, and Avatele Stream locally is 
more than 600 feet lower than the adjacent 
ridges. The entire island would probably have 
been similarly dissected had there been no post- 
caldera volcanism. 
The lowermost 1,000 feet of Laufuti Stream 
on the southern coast is the only perennial 
drainage on Ta’u Island. Laufuti stream valley 
has been cut into the dike complex, tapping 
springs that are fed by ground water trapped 
there by the relatively impermeable dikes. The 
rate of discharge for this stream is on the order 
of thousands of gallons per minute, even during 
periods of minimum rainfall. The upper portion 
of the stream flows only after heavy rains, but 
because of the high rainfall (probably well over 
200 inches per year in this area), water remains 
in small ponds and pools which contain large 
freshwater eels. 
None of the streams on the island is suffi- 
ciently mature to have a floodplain. Alluvium is 
present only in the narrow stream beds and is 
not extensive enough to be mapped separately. 
Many of the stream beds contain boulders up to 
12 feet in diameter. 
beaches and coasts: Marine erosion during 
a long period of volcanic quiescence cut a sea 
cliff approximately 200 feet high around Ta’u 
Island. On the north central coast where pre- 
caldera lavas are exposed the sea cliff cannot be 
distinguished because marine erosion was sub- 
ordinate to stream erosion. On the south central 
coast the cliff is locally as high as 1,200 feet and 
appears to be partly a fault-line scarp. The sea 
cliff is buried under the Faleasao tuff on north- 
western Ta’u, and the Fitiiuta lavas have built 
out in front of the sea cliff on northeastern Ta’u. 
Some of the post-erosional lavas of the Lata 
shield have spilled over this sea cliff. 
Most of the coastline on Ta’u Island consists 
of beaches less than 100 feet wide. Foreshores 
slope 10-13°. Vegetation usually extends to 
within a few feet of the water, because the tidal 
range is low and reefs protect the shore from 
most storm waves. Beachrock is extensively ex- 
posed both above and below present sea level 
along many of the beaches and is being eroded 
at present. The dip of the beachrock is usually 
somewhat less than the foreslope of the present 
beaches, possibly indicating that it was formed 
during a slightly higher stand of the sea. Beach 
material varies in grain size from medium sand 
(Wentworth scale) to gravel, but the beachrock 
is usually fine- to medium-sand size. At Faga, 
Ma’efu, and a few other areas, cobbles and 
boulders are cemented in a matrix of medium to 
coarse sand. 
A bench cut into the Faleasao tuff about 
5 feet above high tide was not observed else- 
where on Ta’u. If this bench was formed at a 
higher sea level, the stand was of relatively 
short duration, because only the easily eroded 
tuff was affected. Present-day waves are destroy- 
ing this bench. 
Ta’u Village is built on a terrace 10 or 12 feet 
above sea level. A terrace at this altitude also 
exists at Faleasao, Faga, Saua, Tufu, Amouli, 
and Si’ufa’alele. These terraces on the southern 
part of the island are composed of sand and 
coral shingle, whereas the others are entirely 
sand. During hurricanes, waves top the terraces 
— as in the hurricane of 1959 when waves de- 
stroyed a trail on the terrace more than 200 feet 
inland at the base of the old sea cliff near Saua. 
Faleasao, the village best protected from waves, 
