A volcano in eastern Russia erupted for the first time in 475 years, prompting a tsunami warning. The Krasheninnikov volcano in Kamchatka became active days after one of the strongest earthquakes ever recorded hit the region.

An 8.8-magnitude earthquake struck off Russia’s eastern coast on late Wednesday morning, local time. The quake triggered tsunami waves across the Pacific that hit Russia, Japan, Canada and parts of the US coast.

Russia’s magnitude 8.8 earthquake spawned serious tsunami warnings, but waves have been moderate so far. Here’s the geological reason why