Adverb taking the 'to' particle
with a crack; with a crash; with a shattering sound
Onomatopoeic or mimetic word
ガラスのコップを流しにおこうとしたら手が滑って、ガシャッと割れた。When I tried to set the glass down in the sink my hand slipped and it shattered to pieces.
Also written がしゃっ