| Anisian(noun, name, volcano, geology) |
| Aptian(noun, name, volcano, geology) |
| Aquitanian(noun, name, volcano, geology) |
| Ardnamurchan(noun, name, volcano, geology) |
| Arenig Fawr(noun, name, volcano, geology) |
| Aristifats Diatreme(expression, name, volcano, geology) |
| Armadillo Peak(expression, name, volcano, geology) |
| Arthur's Seat(expression, name, volcano, geology) |
| Aubrac(noun, name, volcano, geology) |
| Auckland Islands(expression, name, volcano, geology) |
| Azufral(noun, name, volcano, geology) |
| Bajocian(noun, name, volcano, geology) |
| Ball's Pyramid(expression, name, volcano, geology) |
| Banks Peninsula(expression, name, volcano, geology) |
| Barremian(noun, name, volcano, geology) |
| Barrow Hill Local Nature Reserve(expression, name, volcano, geology) |
| Bartonian(noun, name, volcano, geology) |
| Bashkirian(noun, name, volcano, geology) |
| Bass Rock(expression, name, volcano, geology) |
| Bathonian(noun, name, volcano, geology) |