The Rumbleometer is a platform for glass “recovery” floats, sensors,
batteries and a recording package. Each yellow “hardhat” contains a
glass float capable of lifting about 80 pounds. The pressure sensor
accurately records small changes in water pressure caused by
changes in depth. Though lava erupts at 1200 degrees C. (2200 F), the
temperature sensor only detected a change of 4 degrees C. (7 F), due
to rapid cooling by the 2 degree C surrounding seawater. Because of
its close proximity to the lava, the bottom of the hardhat is melted.
The data from the rumbleometer that reveals the most about the eruption is from
the pressure sensor, which recorded vertical movements [changes in depth] of the
instrument. The pressure data show that the lava flow first spread out as a thin
sheet under the instrument. Then the lava flow stopped speading outward and began
to thicken or inflate upward with a solid crust over a molten interior. During this
inflation stage the rumbleometer was actually lifted upward over 3 meters (9 feet)
by the lava flow. Soon thereafter the eruption began to wane and lava drained back
into the eruptive vent, and the rumbleometer was lowered back down, ending up
only 0.5 meters (18 inches) higher than it started. Perhaps most remarkably, all this
took place in the span of only 2 hours. This is the first time that a submarine
eruption has actually been caught in the act, all because an instrument was in the
right place at the right time, and managed to survive!
The rumbleometer was in remarkably good condition after it was rescued. Only the
yellow plastic "hard-hats" that protect the glass ball flotation were melted in a few
spots where they had come in contact with the lava. Amazingly, a temperature
sensor on board the rumbleometer only recorded a 4°C (7°F) increase in
temperature during the eruption! Even though the lava was erupted at a
temperature of about 1200 °C (2200°F), the instrument was kept relatively cool
because it was bathed in frigid seawater at 2°C [36°F] which dissipated most of that
heat. Also the lava quickly forms a solid crust over its molten surface, which greatly
insulates the heat below.