Down Under in Savai’i
This is part of a series of illustrated articles taken from ‘A Visitor’s Field Guide to Savaii’ by geologist, Tuapou Warren Jopling. Tuapou takes tour groups around Savaii and his knowledge is legendary!
TOURING WITH TUAPOU
Today, your tour will take you to the famous site which you may have heard of if you have read the story of ‘Sina and the eel’. Then there is a short but important discussion about results of the Matavanu eruption in the early 1900’s.
Safune, Mangroves and Matalealelo Spring
After a long inland passage from Asau, you reached the coast at Sasina and are now at Safune about to climb a steep hill. This is the eastern scarp of the wide Sataua - Safune slump. The very abrupt 120 0 change in coastline direction is a result of this faulting.
Note all the mangrove trees along the shore. They can grow in seawater but thrive in a brackish habitat. The many freshwater outlets of this area are fed by the Ghyben - Herzberg lens. The walled-in Matalealelo spring is a popular tourist stop with a legend about an eel who fell in love with princess Sina. It grew to enormous size as it followed her from pool to pool around Savai’i’s, last stop being here. She fled to Upolu, the eel followed and was killed by village chiefs. Its dying request was to plant its head. This grew into the world’s first coconut tree. If you don’t believe this, ask a boy to husk a coconut then look at the three round rings on top. A Visitor’s Field Guide to Savai’i – Touring Savai’i with a Geologist
The Mauga Mu Eruption
The Mauga Mu eruption is not an accessible tourist attraction but is discussed here for two reasons; it helps explain Savai’i’s high concentration of small cones; and it was the beginning of an eruptive cycle that culminated with the massive Matavanu eruption.
The short-lived 1902 outbreak was on the high central plateau 4 km east of Mauga Afi, and was shielded from coastal view by the island’s gentle curvature. It was not known if existing cones had erupted or new ones formed. Subsequent investigation showed two closely shaped clusters of spatter cones, together adding seven small cones to the hundreds already extant. This is monogenetic volcanism - new eruptions form new cones, possibly because old cones are underlain by solid basalt plugs. Savai’i’s central plateau is heavily faulted with chains of closely spaced cones lining surface traces (See Figures 9 and 10).
Matavanu’s birth in early August, 1905, was impressive. High lava fountains roared from the ground, quickly built a spatter cone and by early September great surges of incandescent lava were flowing down a river valley to flood the Saleaula coastal plain. This was the first of Savai’i’s historic eruptions to be recorded in detail. Discussion of the Saleaula lava field follows this brief description of the Matavanu volcano.
Matavanu is visible 10 km away from an opening in vegetation along the East Coast road, one kilometre south of Mauga village. Visitors expecting a mighty volcano will be disappointed to see a gently sloping hill set way below the cone- studded skyline. The black band capping this lava cone is the uppermost part of the crater’s western wall. The cone rises about 90 m above surrounding terrain, the summit being aproximately 700 m above sea level.
Matavanu has built over the step fault east of the Sataua - Safune fault block. The 8 km long plantation road from Safotu via Paia to Matavanu is along the downside of a steep 30 m high scarp to the base of the volcano where the scarp is buried under spatter*. Here the road climbs the northern flank and the lush tropical vegetation is replaced by thin scrub allowing great views over northeastern Savai’i. A 300 m track from the road ends at the 50m deep, vertically walled crater. Immature rainforest in and around the crater is attributed to high rainfall.
Discussion about faults providing conduits for rising magma needs clarification. Faults of 30 m or 150 m displacement create spectacular scenery but they are not major structural features and are far too small to have intersected an underlying magma chamber. Savai’i is the pinnacle of an enormous edifice of hotspot origin capped by younger volcanics. This edifice rises 6.8 km from the ocean floor with sub-aerial Savai’i accounting for 3 % of the total structure. The landslide and it’s confining faults are a weak surface expression of considerable disturbance in submarine levels of this eoifice.
* The term spatter refers to falling blobs of molten lava that spread on impact.
ABOUT THE AUTHOR
Tuapou Warren Jopling is an Australian geologist who retired to Savai’i to grow coffee after a career in oil exploration in Australia, Canada, Brazil and Indonesia. Travels through Central America, the Andes and Iceland followed by 17 years in Indonesia gave him a good understanding of volcanology, a boon to later educational tourism when explaining Savai’i to overseas visitors and student groups.
This article is taken from ‘A Visitor’s Field Guide to Savai’i’.