The debris avalanche deposit is long and well preserved. After exiting the collapse scar over its northern opening, it overrode an older scoria cone before coming to rest. The slide, bordered by levee-like structures reaching a height of , formed wide and high lobes. Unlike many debris avalanche deposits, the Lastarria debris avalanche lacks large blocks and has only a few hummocks. The velocity of the avalanche has been estimated to have been over , a fairly high velocity for a volcanic debris avalanche. It is possible that air was entrained in the debris, which thus assumed properties similar to an ignimbrite.