Dikes on a dead Moon
Volcanic landforms, such as sinuous rilles, domes, cones, dark-halo craters, floor-fractured craters, pyroclastic deposits, and even young lava flows are often favourite targets for lunar observers. Scientists have published many studies describing their characteristics and possible origins for these features. Recently, Lionel Wilson (Lancaster University, U.K.) and James Head (Brown University) have proposed a conceptual model that links all these lunar volcanic landforms with different stages in the rise and eruption of magma. While their formal publications are detailed and massive — Head calls one a “doorstop” — a general awareness of their model will enrich your observing with understanding and wonder.
Magma is generated deep within the lunar mantle, and large blobs of it known ascend to within a few hundred kilometres of the surface. The continuing upwelling of additional magma into the diapir increases the pressure at its top until the overlying brittle crustal rocks crack, and a dike of magma fractures its way towards the surface. Whether this dike reaches the lunar surface and what kind of eruption it produces depend on several factors, such as the volume of magma, its eruption rate, duration and gas content, as well as the period in lunar history that it occurred.
