Can you clean up a lava flow after it cools? It's technically possible but difficult, according to AccuWeather.
It can take months or even years for lava flows to completely harden, and they're normally piled up very high when that finally happens. Cleaning the flows up would require the use of heavy equipment, and that process often takes a long time.
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Not to mention, the work can be completely ruined by a new lava flow.
More often than not, people who know they live near an active volcano just find it easier to just adapt and rebuild.