WELLINGTON, March 16 — Scientists claim they have evidence a substantial part of a geological formation, among the great wonders of the 19th century before it disappeared in a volcanic eruption, still exists on the floor of a New Zealand lake.
New Zealand's GNS Science geosciences research institute announced Friday it had backed up findings from June last year to show that a substantial portion of the Pink Terraces — half of the Pink and White Terraces — appeared to have survived the 1886 eruption of Mount Tarawera and was covered by 2 meters of sediment.
The fate of the White Terraces was less certain as they were in a part of the 6 km by 3 km lake that was significantly disturbed by the eruption, said a statement from GNS.
GNS scientists last week undertook sonar and seismic surveys of the floor of the North Island's Lake Rotomahana to remap the topography of lake floor at much higher resolution than a map they compiled last year using free-swimming robotic vehicles.
The new map showed objects less than 50 cm across and revealed previously unknown volcanic craters, fault lines and pockmarks on the lake floor resulting from the 1886 eruption.
"The new lake floor data helps put all existing information about the 1886 eruption and the two geothermal systems under Lake Rotomahana into a much better context," said project leader Cornel de Ronde.
"Most of the newly identified lake floor volcanic features have been hidden for over 100 years," de Ronde said in the statement.
"Their discovery provides much greater insight into the sequence of events that made up the 1886 eruption. In particular, the data shows the volcanic craters and the deep rift that formed when the lake floor unzipped violently during the eruption."
Seismic equipment towed behind a boat released an acoustic vibration that penetrated up to 70 meters below the lake floor and was reflected off geological layers back up to hydrophones towed behind the boat.
"The seismic data has enabled us to strip off about 40 meters of sediment on the lake floor and see the hard post-eruption surface of the lake and other geological structures at depth."
Seismic lines over the location of the Pink Terraces showed hard surfaces at the same depth and in the same location as last year's survey indicated the Terraces would be.
"Last year we found the two bottom tiers of the buttress adjacent to main staircase of the Pink Terraces. This year the seismic data is telling us that there is a 40-meter-wide and three- story-high stack of very hard material exactly where we estimate the Pink Terraces should be.
"We believe this represents a substantial portion of the Pink Terraces, although we were not able to determine their state of preservation. We were unable image individual terraces."
The new data would advance the knowledge and understanding of Mount Tarawera-type eruptions not just in New Zealand, but internationally and of sub-lake floor geothermal systems.
"Very few volcanic lakes in the world could match this level of detail," said de Ronde.
The Pink and White Terraces were two sets of scalloped and cascading silica terraces were separated by several hundred meters.
The two formerly glistening terraces were formed on the shores of the lake, where the silica rich waters were warmed by the magma beneath.
In the late 19th century, the cascading terraces attracted people from all over the world.
The White Terraces were the larger and stretched to a height of 30 meters, forming a 240-meter face. Visitors could walk up to a crater platform where they could bathe in the clear blue waters in naturally-formed basins up to 3 meters deep.
Although the Terraces were recorded in images and writing, their exact whereabouts had remained a mystery until their rediscovery last year. (PNA/Xinhua)