Underwater noise from submarine turbidity currents

Abstract

Submarine landslides and associated turbidity currents can be orders of magnitude larger than their terrestrial equivalents. Their prevalence globally is hugely underrepresented by in situ observations. In addition to their importance in mass transport and morphologic change they can pose significant threat to coastal communities and subsea infrastructure. This presentation focusses on noise measurements from turbidity currents flowing down the face of a fjord delta and how they can inform the use of passive acoustics as a tool for future observations of these under sampled phenomena. Noise was measured underwater at frequencies from 1 to 1200 kHz. The noise spectra are consistent with sound generation by collisions among sand-sized particles within the turbidity current, also known as acoustic sediment-generated noise or SGN. The spectra from the leading head of the current extend to higher frequencies than those from the trailing body, indicating that collisions were between finer-grained particles in the head and coarser-grained particles in the body. Noise intensity increased 100-fold for a two-fold increase in current head speed, consistent with the expected collision rate for granular materials in the high-flow gas-like phase and highly turbulent particle-laden flows.