What is the most "dangerous" active coastal volcano globally?
Please see the Decade List. Most of those volcanoes are located along coastlines.
Anak Krakatoa is an island and caldera in the Sunda Strait situated between the islands of Java and Sumatra in the Indonesian province of Lampung. On 29 December 1927 Anak Krakatau, or "Child of Krakatoa", emerged from the caldera formed in 1883 by the explosive volcanic eruption which destroyed the island of Krakatoa. There has been sporadic eruptive activity at the site since the late 20th century. An eruption of the volcano on 22 December 2018 caused a deadly tsunami. On 31 December 2018 the disaster agency stated the tsunami's death toll as 437, with 14,059 injured. This makes the eruption the deadliest volcanic eruption of the 21st century.