A rarely seen plume of sulfur-rich surface gas nearly 200 meters high was spotted off the coast of Guishan Island in Yilan County Sunday.

Footage of the gas plume billowing from an underwater fumarole was captured by Chien Feng-chun (簡逢均), a tour guide aboard the Hung Chi whale-watching boat.

The Northeast and Yilan Coast National Scenic Area Administration under the Tourism Bureau said that the plume was likely caused by rocks or tectonic activity unblocking or deforming hydrothermal vents on the seabed around Guishan Island, also known as Turtle Island.

According to the administration's website, the plumes of sulfur-rich gas are just one of several natural spectacles that can be seen on Guishan Island and the surrounding waters, along with underwater hot springs and the stalactites and stalagmites of Eyeglass Cave.

The last time a cloud of sulfur smoke was spotted from the island was on Jan. 10 this year.