1808/1809 mystery eruption
1808 CE.
Shown on the map at 0.000°, -160.000°.
The 1808 mystery eruption is one or potentially multiple unidentified volcanic eruptions that resulted in a significant rise in stratospheric sulfur aerosols, leading to a period of global cooling analogous to the Year Without a Summer in 1816.
Text from the Wikipedia article 1808 mystery eruption, licensed CC BY-SA 4.0.