This site has speculated that a cataclysmic eruption of a supervolcano (see topic ‘Science and the Sixth Seal’ for a more detailed discussion) could be how God decides to manifest the opening of the Sixth Seal, as described in Revelation 6:12-14:
And I beheld when he had opened the sixth seal, and, lo, there was a great earthquake; and the sun became black as sackcloth of hair, and the moon became as blood; And the stars of heaven fell unto the earth, even as a fig tree casteth her untimely figs, when she is shaken of a mighty wind. And the heaven departed as a scroll when it is rolled together; and every mountain and island were moved out of their places.
We have discussed the supervolcano in Japan, at Sakurajima, as well as the US supervolcano in Long Valley, California. However, a European supervolcano has recently become active.
http://www.sciencealert.com/the-supervolcano-that-caused-one-of-the-biggest-eruptions-in-history-has-started-to-stir
Needless to say, should this supervolcano, located in southern Italy, erupt in a cataclysmic fashion, it would surely serve as God’s final warning that we are truly in the End of Days, and that things are about to get very serious indeed.