Effects of igneous bodies on modification of modern slope morphology: Insights from the continental slope offshore Dongsha Islands, South China Sea

A statistical analysis for the morphological parameters extracted from numerous seismic profiles, and a highresolution seismic study of the southeastern slope of the Dongsha Islands(South China Sea) with water depth between approximately 500 and 3 100 m, has revealed the variation of morphological features due to the intrusion of igneous bodies and associated sedimentary processes. Three types of the continental slope are distinguished:(1) a rough and steep slope with multiple igneous bodies(Type 1),(2) a relatively smooth and gentle slope with the single igneous body(Type 2), and(3) a smooth and gentle slope without igneous bodies(Type 3). These igneous bodies, formed in the post-seafloor spreading of the South China Sea, are often characterized by high positive seismic amplitudes, and chaotic reflections with complex shapes. The igneous bodies in Type 1 separated the slope into two or more upper sub-sags and a lower main-sag, in which the sub-sags and main-sag could be filled with sediments transported by alongslope bottom currents at the same time. Whereas, the igneous body in Type 2 just separated the slope into an upper sub-sag and a lower main-sag, in which the sediments could be transported into the lower main-sag only after the upper sub-sag has been filled up. Type 3 represents a normal slope with common clinoform progradation. The modern slope morphologies in the study area are the results of adjustments of the continental slope due to the intrusion of igneous bodies and associated sedimentary processes. The distinctions among three types of modern slope morphologies indicate different depositional conditions and adjustments of slope morphologies.

Discharge characteristics of leader inception and development under 10 m long air gap—experimental observation and simulation results

The physical mechanism of leader formation and development is not well understood.In this study,we present experimental and simulation results obtained with a 10 m long air gap discharge.A 10 m outdoor discharge experiment is carried out to obtain the current,voltage,and optical image during the leader discharge process.Four different impulse voltages were applied to the rod‐plane gap.The measured current is used as an input for a plasma model,then the temperature and electric field could be calculated.The simulation results show that the temperature of the streamer stem during the dark period may exceed 2000 K.In addition,the critical charge required for leader initiation can be as low as 0.27μC for a 10 m air gap.The channel temperature is relatively stable in the process of leader development,which is maintained at about 4500 K.The electron density is about 0.5–3�1020 m-3,and the discharge channel conductivity fluctuates in the range of 1–10 S/m for the leader current between 1 and 2 A.A long dark period is tended to be associated with a higher injected charge by the first streamer.It is inferred that the voltage increments during the dark period play an important role in promoting streamer‐to‐leader transition,except for temperature and the injected charge.