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How did lava flows shape Mercury’s smooth plains?

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Messenger: Mercury — Mercury Mercury as seen by the Messenger probe, January 14, 2008. This image shows half of the hemisphere missed by Mariner 10 in 1974–75 and was snapped by Messenger's Wide Angle Camera when it was about 27,000 km (17,000 miles) from the planet.

Lava flows have played a significant role in shaping Mercury’s smooth plains through a process of resurfacing, which involves the covering or destruction of rough, older topography to create a more level surface.1

Under the influence of gravity, lava originating from the planet's interior flows toward lower elevations. This material collects in depressions, filling them to higher levels as more volume is added. Evidence for this volcanic activity is visible in several relatively youthful plains, where older craters appear to have been "filled to the brim" by these flows, similar to volcanic features observed on the Moon and Mars.1

While the formation of widespread intercrater plains is more difficult to evaluate due to their age—which may have resulted in the erosion or obliteration of distinct volcanic features—these plains are believed to be responsible for erasing a significant portion of smaller craters on the planet's surface.1