diapir

A diapir ( [1]) (French, from Greek diapeirein, to pierce through) is an intrusion caused by buoyancy and pressure differentials. The term was introduced by the Romanian geologist Ludovic Mrazek, who was the first to undertand the principle of salt intrusion and plasticity. Diapirs may include igneous structures, but are more commonly applied to non-igneous, relatively cold materials, such as salt domes and mud diapirs; diapirism is thought to occur on Enceladus. A diapir is any relatively mobile mass that intrudes into preexisting strata. A lava lamp is an example of a diapir.
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Noun
1. a domed rock formation where a core of rock has moved upward and pierced through the more brittle overlying strata
(hypernym) geological formation, formation
(classification) geology