A<unk>  is an opening, or rupture, in a planet's surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface.<unk> c activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time.<unk> es are generally found where tectonic plates are pulled apart or come together. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of<unk> es caused by "divergent tectonic plates" pulling apart; the Pacific Ring of Fire has examples of<unk> es caused by "convergent tectonic plates" coming together. By contrast,<unk> es are usually not created where two tectonic plates slide past one another.<unk> es can also form where there is stretching and thinning of the Earth's crust (called "non-hotspot intraplate<unk> sm"), such as in the African Rift Valley, the Wells Gray-Clearwater<unk> c Field and the Rio Grande Rift in North America and the European Rhine Graben with its Eifel<unk> es.<unk> es can be caused by "mantle plumes". These so-called "hotspots" , for example at Hawaii, can occur far from plate boundaries. Hotspot<unk> es are also found elsewhere in the solar system, especially on rocky planets and moons.
Volcano
Pagetoid
Choana
Symphoricarpos
Ergoloid
Samarium 
Deaf-mute
Chigger