Eiro's palm struck at Krog's forearms as he directed the power of the mountain-breaker into his hand. But of course, Eiro didn't want to use the entirety of that power on Krog, since that could do more damage than he'd like. Krog was still in the middle of learning proper defensive techniques, so Eiro couldn't expect him to be able to block an arcane card's powers yet.
So, instead, he directed a portion of the power toward his hand, and then the rest into his feet to make the power spread thin through the ground. As he controlled it well enough, it didn't really cause any issues with the ground either. A few pebbles were thrown around, but that was the most of it. As for Krog, his defense was broken pretty quickly. The chains wrapped around his arms managed to survive the hit, but Krog's arms were thrown to the side and he was pushed off-balance. He was completely open for a follow-up attack.