and were examined by Soule et al. (2012) in order to determine their degassing
process. Measurements were made concerning the vesicularity, crystallinity, and
the volatile and helium contents of the collected samples. Observations on the CO 2
loss from the melt and a subsequent bubble growth suggest some constraints for
the dynamics of eruption. Based on the amount of CO 2 exsolution between
proximal and distal samples, Soule and his colleagues estimated the duration of the
eruption to be about 30 h (Soule et al. 2012). For a flow thickness of about 1.5 m, a
mean eruption rate of *25 m
3 s/km was proposed (Soule et al. 2007). This
eruption rate is similar to that of the Hawaiian lava flows. These results showed
that the most recent EPR eruption must have occurred during a series of shortduration pulses rather than during a continuous eruptive event. A lava flow
velocity of 0.12 m/s was estimated for the early eruption; however, that flow
velocity rapidly declined to 0.02 m/s for the entire period of the eruptive event.
Popping Rocks
The first time I witnessed the release of gas that had been trapped in volcanically
erupted material was in 1972 during the Midlante cruise with the N. O. JEAN
CHARCOT. The MIDLANTE cruise was a preparatory survey cruise for project
FAMOUS in the North Mid-Atlantic ridge near 36°49
0 N and 33°15
0 W. After a
dredge haul was collected on the axis of the rift valley at 2480 m depth, Jean
Francheteau and I were looking at the rocks that had been dumped on the backdeck. To our surprise, we heard noises that sounded like pops, just like the sound
of popcorn being cooked. We realized we were dealing with samples that were
jumping and popping due to the pressure of degassing. We called them ‘‘popping
rocks’’. Suddenly, an oval-shaped rounded glassy rock fragment shot up into the
air a couple meters away from us. Then several other chunks did the same thing.
We figured out that the rocks were degassing because of the difference in atmospheric pressure when they were brought to the surface from the sea floor’s depths.
We immediately stored these samples inside a rough-woven potato sack along with
a tape-recorder inside the bag to record how long it would take the samples to
degas. The bag was stored in the science laboratory on board the ship. Unfortunately, we were not equipped with any sealed gas containers to store the samples
and collect the gas that was being released, but we made sure to bring such
material for future missions. The rocks exploded and popped for 3 days giving off
a sharp smell of rotten-eggs as they split open (Photo 5.14). This preliminary
discovery was reported in an article published in Nature (Hekinian et al. 1973) .
When the popping rocks dredged from the 1972 cruise were taken back to a
specialized CNRS (Centre national de Recherche Scientifique) laboratory in Paris
(Institut de Physique du Globe), M. Chaigneau, a specialist in gas analyses, discovered that the volatile content of these rocks consists mainly of carbon dioxide
(39–45 %) and carbon monoxide (13–17 %), hydrogen dioxide (27–35 %) and
sulfide oxides (2–11 %) (Chaigneau et al. 1980). Later, Marty et al. (1983) studied
Volatiles and Gas in Magma
127
process. Measurements were made concerning the vesicularity, crystallinity, and
the volatile and helium contents of the collected samples. Observations on the CO 2
loss from the melt and a subsequent bubble growth suggest some constraints for
the dynamics of eruption. Based on the amount of CO 2 exsolution between
proximal and distal samples, Soule and his colleagues estimated the duration of the
eruption to be about 30 h (Soule et al. 2012). For a flow thickness of about 1.5 m, a
mean eruption rate of *25 m
3 s/km was proposed (Soule et al. 2007). This
eruption rate is similar to that of the Hawaiian lava flows. These results showed
that the most recent EPR eruption must have occurred during a series of shortduration pulses rather than during a continuous eruptive event. A lava flow
velocity of 0.12 m/s was estimated for the early eruption; however, that flow
velocity rapidly declined to 0.02 m/s for the entire period of the eruptive event.
Popping Rocks
The first time I witnessed the release of gas that had been trapped in volcanically
erupted material was in 1972 during the Midlante cruise with the N. O. JEAN
CHARCOT. The MIDLANTE cruise was a preparatory survey cruise for project
FAMOUS in the North Mid-Atlantic ridge near 36°49
0 N and 33°15
0 W. After a
dredge haul was collected on the axis of the rift valley at 2480 m depth, Jean
Francheteau and I were looking at the rocks that had been dumped on the backdeck. To our surprise, we heard noises that sounded like pops, just like the sound
of popcorn being cooked. We realized we were dealing with samples that were
jumping and popping due to the pressure of degassing. We called them ‘‘popping
rocks’’. Suddenly, an oval-shaped rounded glassy rock fragment shot up into the
air a couple meters away from us. Then several other chunks did the same thing.
We figured out that the rocks were degassing because of the difference in atmospheric pressure when they were brought to the surface from the sea floor’s depths.
We immediately stored these samples inside a rough-woven potato sack along with
a tape-recorder inside the bag to record how long it would take the samples to
degas. The bag was stored in the science laboratory on board the ship. Unfortunately, we were not equipped with any sealed gas containers to store the samples
and collect the gas that was being released, but we made sure to bring such
material for future missions. The rocks exploded and popped for 3 days giving off
a sharp smell of rotten-eggs as they split open (Photo 5.14). This preliminary
discovery was reported in an article published in Nature (Hekinian et al. 1973) .
When the popping rocks dredged from the 1972 cruise were taken back to a
specialized CNRS (Centre national de Recherche Scientifique) laboratory in Paris
(Institut de Physique du Globe), M. Chaigneau, a specialist in gas analyses, discovered that the volatile content of these rocks consists mainly of carbon dioxide
(39–45 %) and carbon monoxide (13–17 %), hydrogen dioxide (27–35 %) and
sulfide oxides (2–11 %) (Chaigneau et al. 1980). Later, Marty et al. (1983) studied
Volatiles and Gas in Magma
127