|Styx Vent does its part in supplying material for the growth of NW Rota-1.|
|Rota Summit: Hydrophone, biologic experiment and marker precariously hold onto what’s left of the summit of NW Rota-1 at 518 meters. Black area is where Jason triggered small sediment slide when deploying instruments.|
NW Rota is more or less a “typical” composite submarine volcano found along the Mariana volcanic arc. During its early growth in deep water eruptions produced primarily lava flows. Several smaller deeper submarine cones composed primarily of lava flows are found ~12 nautical miles (~20 km) east of NW Rota. As it grew shallower eruptive activity became more explosive as the pressure holding the gas dissolved in the magma lessened. This transition led to a gradual change in the form of the volcano because volcanic fragments such as ash and larger pieces can only build out to the “angle of repose” after which the material sloughs away into deeper water building out the flank of the volcano. We see this process on a small scale when Jason triggers slides in the newly deposited volcanic sand near the eruption sites. Yesterday we saw small scale mass movements at Styx vent when it suddenly became very active. In fact, the Jason was “shoved” away from the vent as material cascaded downslope in front of us. The large landslide that occurred here during the past year is part of this long term process of volcano construction.
|Southern flank of NW Rota-1: White stained angular blocks on top of debris flow from summit litter slope near where we “heard” one of the lost moorings.|
Some arc volcanoes undergo much more catastrophic events. A volcano called West Rota lying ~ 16 nautical miles (~30 km) SE of NW Rota had a very large eruption ~40,000 years ago when the entire top of the volcano was removed during an explosive eruption that formed a caldera (large crater) similar in size to Crater Lake in southern Oregon.
We have to appreciate that we are only looking at a short chapter in the life history of NW Rota. How long this “growth spurt” will last is anyone’s guess.
NOAA Pacific Marine Environmental Laboratory