September 12, 1866 Eruption of Ofu-Olosega

1866, September 12, Samoan Islands. An underwater volcano erupted in the vicinity of the Manua Islands. The first indications of it were weak shocks, felt on September 7 by the inhabitants of the islands of Tau and Olosega, which are part of that archipelago. These shocks occurred at an average of four per hour, and the vibrations continued into the following day. Thirty-nine shocks occurred during the night of September 9.

After dinner on the 12th a disturbance in the sea commenced at a distance of approximately 3 km (1 1/2 miles) from the island of Olosega and 8 km (4 1/2 miles) from the island of Tau...The destruction continued all that day and through part of the next. This was followed by an underwater eruption with its usual manifestations. On the 15th of September the eruption was repeated, and each hour approximately 50 eruptions occurred...During this time large pieces of lava floated up to the surface of the ocean, and tremors were felt on the islands. A column of thick smoke, rising to a height of about 600 m (2,000 ft), completely darkened the sky.

Although the eruption did not reveal open flames, gleams of fire could be observed on two or three occasions. The sea was extremely disturbed and for a distance of 20 km (10 miles) glittered with a phosphorescent light. Many dead fish floated to the surface and were cast upon the shore.

After three days, the frequency of the eruptions began to abate, although even on the 11th of November three or four explosions per hour could be counted. The products of the eruption were not thrown up to such a significant height as previously, now no higher than 5-10 m (20-30 feet). The condition of the vegetation on the Manua Islands suggests that this area had not seen very severe eruptions for at least 80-100 years.

(above from reference #415).

Start Date: 1866 Sep 12, Stop date: 1866 Nov 15 ± 5 days. Certainty Confirmed, VEI 2, Historical Observations. Submarine vent 3 km SE of Olosega. (reference #2432)