Complex sentence: When drilling in temperate ice, thermal drills have an advantage over electromechanical (EM) drills: ice melted by pressure can refreeze on EM drill bits, reducing cutting efficiency, and can clog other parts of the mechanism.
Split into simpler sentences: When drilling in temperate ice, thermal drills have an advantage over electromechanical (EM) drills. Ice melted by pressure can refreeze on EM drill bits, reducing cutting efficiency, and can clog other parts of the mechanism.