We propose a network flooding algorithm for wireless ad hoc networks based on a pure physical layer design. The idea is to let the nodes in the network act as asynchronous relays to a specific leader, generating an avalanche of signals which we call opportunistic large array (OLA). The accumulation of power in the medium coming from the interfering signals constructs a signal space for each receiver node that can be acquired through training or blindly. The acquisition of the signal space allows the leader to flood the network without higher layer intervention. Compared to other approaches that are based on the network layer and use point-to-point links to flood the network, we show that the proposed flooding algorithm achieves higher efficiency in the end-to-end delay and has a higher delivery ratio due to the accumulation of energy. In fact, a major contribution of this paper is mapping the multiple-access network problem into a single user problem and then using signal processing techniques to solve it instead of networking algorithms.