*3.2. Gas Distribution*

**Figure 6.** Experimental photographs showing the ripples. (**a**) Top view; (**b**) Side view. A sample portion of the soil approximately 10 cm in the upper layer was taken after the end of the experiment. It was found that there was a large number of gas holes in the vertical section of the soil sample (Figure 7). The gas holes in the soil were distributed in a horizontal or inclined and zonal manner rather than being uniform (Figure 8), and even a gas channel existed. Within a depth *3.2. Gas Distribution* 

*3.2. Gas Distribution* 

*3.2. Gas Distribution* 

ranging from 3 cm to 4 cm and from 8 cm to 10 cm, the number of pores was greater than 100, while the holes in other depth ranges were less than 30. The area where the pores were densely distributed was consistent with the sliding surface of the soil mass. manner rather than being uniform (Figure 8), and even a gas channel existed. Within a depth ranging from 3 cm to 4 cm and from 8 cm to 10 cm, the number of pores was greater than 100, while the holes in other depth ranges were less than 30. The area where the pores were densely distributed was consistent with the sliding surface of the soil mass. from 3 cm to 4 cm and from 8 cm to 10 cm, the number of pores was greater than 100, while the holes in other depth ranges were less than 30. The area where the pores were densely distributed was consistent with the sliding surface of the soil mass. from 3 cm to 4 cm and from 8 cm to 10 cm, the number of pores was greater than 100, while the holes in other depth ranges were less than 30. The area where the pores were densely distributed was consistent with the sliding surface of the soil mass.

soil sample (Figure 7). The gas holes in the soil were distributed in a horizontal or inclined and zonal

manner rather than being uniform (Figure 8), and even a gas channel existed. Within a depth ranging

*J. Mar. Sci. Eng.* **2019**, *7*, x FOR PEER REVIEW 6 of 10

*J. Mar. Sci. Eng.* **2019**, *7*, x FOR PEER REVIEW 6 of 10

*J. Mar. Sci. Eng.* **2019**, *7*, x FOR PEER REVIEW 6 of 10

A sample portion of the soil approximately 10 cm in the upper layer was taken after the end of

A sample portion of the soil approximately 10 cm in the upper layer was taken after the end of

A sample portion of the soil approximately 10 cm in the upper layer was taken after the end of

**Figure 7.** Photographs showing the gas holes in different scales. **Figure 7.** Photographs showing the gas holes in different scales. **Figure 7.** Photographs showing the gas holes in different scales. **Figure 7.** Photographs showing the gas holes in different scales.

**Figure 8. P**hotographs showing the ribbon of gas holes. **Figure 8. P**hotographs showing the ribbon of gas holes. **Figure 8.** Photographs showing the ribbon of gas holes. **Figure 8. P**hotographs showing the ribbon of gas holes.

The gas holes in the soil sample were distributed in an oblique and zonal manner at a distance of 100–110 cm from the left wall of the flume, at an angle of approximately 30°–40° with the horizontal plane. The closer they were to the surface of the soil, the smaller the inclination. The distribution of gas holes (Figure 9) was substantially consistent with that of sliding surfaces. Previous studies confirmed fine-particle migration due to external actions, such as waves [22,24,25]. However, this experiment offered the first evidence of possible gas migration due to wave action. The presence of The gas holes in the soil sample were distributed in an oblique and zonal manner at a distance of 100–110 cm from the left wall of the flume, at an angle of approximately 30°–40° with the horizontal plane. The closer they were to the surface of the soil, the smaller the inclination. The distribution of gas holes (Figure 9) was substantially consistent with that of sliding surfaces. Previous studies confirmed fine-particle migration due to external actions, such as waves [22,24,25]. However, this experiment offered the first evidence of possible gas migration due to wave action. The presence of gas may serve as a primer for submarine slope failure [26]. The gas holes in the soil sample were distributed in an oblique and zonal manner at a distance of 100–110 cm from the left wall of the flume, at an angle of approximately 30◦–40◦ with the horizontal plane. The closer they were to the surface of the soil, the smaller the inclination. The distribution of gas holes (Figure 9) was substantially consistent with that of sliding surfaces. Previous studies confirmed fine-particle migration due to external actions, such as waves [22,24,25]. However, this experiment offered the first evidence of possible gas migration due to wave action. The presence of gas may serve as a primer for submarine slope failure [26]. The gas holes in the soil sample were distributed in an oblique and zonal manner at a distance of 100–110 cm from the left wall of the flume, at an angle of approximately 30°–40° with the horizontal plane. The closer they were to the surface of the soil, the smaller the inclination. The distribution of gas holes (Figure 9) was substantially consistent with that of sliding surfaces. Previous studies confirmed fine-particle migration due to external actions, such as waves [22,24,25]. However, this experiment offered the first evidence of possible gas migration due to wave action. The presence of gas may serve as a primer for submarine slope failure [26].

gas may serve as a primer for submarine slope failure [26].

**Figure 9.** Schematic diagram showing the direction of gas distribution. **Figure 9.** Schematic diagram showing the direction of gas distribution. **Figure 9.** Schematic diagram showing the direction of gas distribution. **Figure 9.** Schematic diagram showing the direction of gas distribution.
