While Clark felt that he could not use the same degree of strength as he could if he was better rested, his speed did not slow. He was sprinting back toward Solar city and was thanking the lord of creation that it was this pair of cities that were closest to one another.
The massive burst of flames and magma that had come from the city had been a clear attack. While he was not worried that Professor Wright would be safe, he was worried about those fleeing the city.
Solar Academy City was on a massive lake of lava. The main thing that kept it solid was the fact that tamers and beasts worked to be able to maintain their city's safety. Therefore, such an explosion would definitely be enough to shake the foundation of the city and even possibly sink it in to the depths of lava below them.
drop those golden tickets!