While the exact age of Mount Yasur is unknown, it's estimated to be around 800,000 years old.

This age is based on:

* Volcanic activity: Mount Yasur has been continuously active for a long period, with historical records dating back to the 18th century.

* Geological studies: Studies of the volcano's structure and surrounding rock formations suggest a significant age.

However, it's important to note that this is an approximation. Precise dating of volcanic formations is complex and involves various methods like radiometric dating, which can provide more accurate age estimates.