A drop in sulfur dioxide released from an eruption on Kilauea volcano's east side might mean the eruption is finally running out of gas after 27 years, scientists say.

Sulfur dioxide helps drive volcanic activity, and the decrease in the gas on the east rift zone could signify the end of the eruption that began in January 1983.

Compare: In September 2008 the eruption was spewing about 2,600 metric tons of sulfur dioxide per day. On April 23, the most recent reading, the sulfur dioxide level was 520 metric tons per day.

Part of the reason might be a second eruption at Halemaumau fire pit, which began in March 2008.

Sulfur dioxide emissions at the summit increased from 200 tons per day before the eruption to 800 tons per day afterward.

More sulfur dioxide at the summit could mean less of the gas remains in the molten lava to carry it to the east rift zone eruption at Puu Oo, said geophysicists at the Hawaiian Volcano Observatory.

Sulfur dioxide and other gases dissolved in magma help drive the molten rock to the earth's surface, much like a shaken soda bottle that fizzes. That is because gas in a liquid will push the liquid to a lower-pressure area.

Scientists are watching carefully to see the effect of the summit eruption on the east rift zone because it is the first time they have observed two sustained volcanic eruptions on Kilauea volcano, said Janet Babb, geologist and spokeswoman for the observatory.

An eruption's strength can also be measured by lava flow, but that has been a problem at the east rift zone, where the flows are mostly underground.

Scientists have not had a consistent lava tube with a skylight for months, Babb said. To get a lava measurement, scientists need a lava tube with an opening, or skylight, that they can peer in to estimate the amount of lava inside.

While lava still creeps along from the east rift zone toward the ocean to the south, the last lava tube system transporting lava directly into the ocean died nearly four months ago, the observatory said.

“;All these changes suggest a sputtering of the east rift activity,”; an observatory statement said. “;The east rift eruption appears to be running low on gas while the summit eruption continues strongly.”;