We investigate the interaction between Yucca Mountain repository drifts (horizontal emplacement tunnels) and a hawaiitic magma in three scenarios: (1) a single feeder dike that extends above an intersected drift; (2) same as 1 but with an additional secondary dike extending upward from the drift; (3) same as 1 with the drift initially filled with pyroclasts and gas under high pressure which is then decompressed as might happen if some blockage is rapidly removed in the volcanic system above the drift. Our results indicate that the drift is likely to experience dynamic pressure waves from expansion of rising magma and subsequent pyroclastic flows, with a maximum possible dynamic pressure of ~107 Pa. A secondary dike above the drift has negligible effects upon the flow dynamics. In the third scenario, particles settle fairly quickly along the floor of the drift, suggesting that a swift decompression within the drift will not be able to remove all the magmatic materials.