Episode 51 . . . began on the afternoon of 7 March, four days after an intrusion in the upper East rift marked the end of the previous episode. A new fissure vent developed on the W flank of Pu`u `O`o, directly upslope from the E-50 vent, and lava within Pu`u `O`o rose to within 55 m of the rim. Lava production apparently stopped at about 2100, but resumed by midnight. Fieldwork the next day revealed an active fissure 34 m long with a spatter rampart 6 m high. Lava ponded W of the vent, while channelized flows moved south and new lava briefly filled the E-50 aa channel.

Lava production stopped at least four times during the following weeks. Active periods that sometimes lasted little more than a day were separated by repose intervals of 16-67 hours. Summit tilt consistently showed slight inflation during repose periods. The E-51 vent built a small shield on the W flank of Pu`u `O`o. Most of the small braided lava streams that covered the shield were fed by a summit lava pond, on the uprift (W) side of the active fissure. Large flows advanced in all directions from the new vent, expanding the W and S margins of the E-50-51 lava field (figure 85). Some flows emerged from the vent without passing through the pond. These wrapped around the base of Pu`u `O`o. On 13 April, a large pahoehoe flow was moving south and was nearing a forested area.

The level of lava inside Pu`u `O`o fluctuated between 35 and 60 m below the spillway on the crater rim, sustaining frequent gas-piston events and vigorous spattering. The lava level apparently dropped during two of the repose periods, then rose with renewed activity at the E-51 vent. On 12 April, several lava overflows briefly covered the crater floor before lava again retreated deeper into the vent.

Geological Summary. Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Information Contacts: T. Mattox, HVO.