TAIPEI (Taiwan News) — A large plume of smoke at Turtle Island, said to be the largest in 24 years, surprised tourists and locals in Yilan County on Sunday (Nov. 21).

Tourists aboard the whale-watching boat the Hung Chi, who caught the moment with their phones, also noticed a rainbow appearing along with the smoke, CNA reported. Yilan County resident Wei Yuan-shun (韋元順) captured a photo of the pillar of smoke near the “turtle’s head” all the way from Dongshan Township’s Renshan Botanical Garden 31 kilometers away.

Chien Feng-chun (簡逢均), tour guide aboard the Hung Chi, told CNA that since a massive outburst on Oct. 28, smoke has continued to flow from the island. On Sunday, it reached almost as high as the turtle’s head, which has an altitude of 239 meters.

Chien said older residents of the area had told him that sometime before 1951, smoke once reached higher than the turtle’s head.

Smoke at Turtle Island captured from Dongshan Township. (Wei Yuan-shun photo)

Once considered one of Turtle Island’s “Eight Views,” the sulfurous smoke disappeared in 2004 after an earthquake sealed off ventilation holes and did not reappear until March of this year, per CNA.

Hsu Yuan-feng (許源豐), head of the Northeast and Yilan Coast National Scenic Area Office’s security team, was cited as saying that the return of smoke at Turtle Island may stem from earthquakes widening underwater gaps that allow gas to escape. Another reason may be falling rocks breaking open such gaps.

He said while he has never seen so much smoke at the island since he took up the post in 1997, it is a sign of normal volcanic activity.