Current visualization technology implemented in the software for 2D sonars used in marine research is limited to slicing whilst volume visualization is only possible as post processing. We designed and implemented a system which allows for instantaneous volume visualization of streamed scans from 2D sonars without prior resampling to a voxel grid. The volume is formed by a set of most recent scans which are being stored. We transform each scan using its associated transformations to the view-space and slice their bounding box by view-aligned planes. Each slicing plane is reconstructed from the underlying scans and directly used for slice-based volume rendering. We integrated a low frequency illumination model which enhances the depth perception of noisy acoustic measurements. While we visualize the 2D data and time as 3D volumes, the temporal dimension is not intuitively communicated. Therefore, we introduce a concept of temporal outlines. Our system is a result of an interdisciplinary collaboration between visualization and marine scientists. The application of our system was evaluated by independent domain experts who were not involved in the design process in order to determine real life applicability.