An undersea volcano approximately 7 miles southwest of the main island of Tongatapu erupted this week in a spectacular display, spewing smoke, steam and ash thousands of feet above the surface of the South Pacific ocean.

First signs of the eruption began appearing on Monday after a series of earthquakes were felt in the capital city of Nuku’alofa. By Wednesday, a new island — obscured by smoke and steam to ocean observers — appeared on satellite photographs.

Precautionary tsunami alerts were issued shortly after the eruption began, but as of Thursday night, no damage or casualties were reported on the main island. Scientists note that the situation could change if the volcano continues to erupt or additional seismic activity occurs.

Tonga is an archipelago of 171 islands, 48 of which are inhabited. Nearly 70 percent of its 115,000 inhabitants live on the main island.

Tonga lies in the Pacific Ring of Fire, where continental plates in the Earth’s crust meet and volcanic and seismic activity are frequent. Clustered around Tonga are approximately 35 volcanoes, the most recent having erupted in 2002.

Worldwide, submarine volcanoes account for approximately three-fourths of all magma output. Most are located in deep waters where high pressure prevents water from boiling and cold temperatures quickly turn magma to glass. As a result, deep sea volcanoes can be difficult to detect. Not so with eruptions in shallower waters like the current Tonga event. After the smaller 2002 eruption, ash was detected 1,200 miles away in Australia.

Undersea Volcano Erupts Near Tonga in the Pacific Ring of Fire: March 18, 2009