Simplify the following text for a Grade 8 native English-speaking person.
Original: They are also often associated with lava volcanoes ; in the case of such close proximity , mud volcanoes emit incombustible gases including helium , whereas lone mud volcanoes are more likely to emit methane .
Simplified: They are also often linked with lava volcanoes as well . However , instead of spitting out magma , mud volcanoes spit out gases like methane and carbon dioxide .