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In the absence of high tidal range and extremely strong marine energy, the [[distributary channel]] pattern is often one of seaward [[bifurcation]] ([[:file:M31F16.jpg|Figure 1]]). Because of this bifurcating channel pattern, the distributary-mouth bars at each of the river mouths often merge and form a near-continuous sand strip around the entire periphery of the delta. Shallow offshore slopes and low wave and tide action favor this type of distributary pattern, and turbulent diffusion within the water mass becomes restricted to the horizontal. Bottom friction plays a major role in causing effluent deceleration and expansion. Initially a broad, arcuate radial bar will form at the mouth. However, as deposition on the bar continues, natural subaqueous levees will develop beneath the lateral boundaries of the expanding effluent, where velocity gradients are generally steepest. Development of subaqueous levees tends to inhibit further increases in effluent expansion, so that with continuing bar accretion continuity can no longer be maintained simply by increasing effluent width. As the central part of the bar grows upward, channelization develops along the threads of maximum turbulence, which tend to follow the subaqueous levee. This process results in formation of a bifurcating channel, which has a triangular middle ground shoal separating diverging channel arms. This type of channel pattern is well displayed in the high-altitude photograph shown as [[:file:M31F16.jpg|Figure 1]].

In the absence of high tidal range and extremely strong marine energy, the [[distributary channel]] pattern is often one of seaward [[bifurcation]] ([[:file:M31F16.jpg|Figure 1]]). Because of this bifurcating channel pattern, the distributary-mouth bars at each of the river mouths often merge and form a near-continuous sand strip around the entire periphery of the delta. Shallow offshore slopes and low wave and tide action favor this type of distributary pattern, and turbulent diffusion within the water mass becomes restricted to the horizontal. Bottom friction plays a major role in causing effluent deceleration and expansion. Initially a broad, arcuate radial bar will form at the mouth. However, as deposition on the bar continues, natural subaqueous levees will develop beneath the [[lateral]] boundaries of the expanding effluent, where velocity gradients are generally steepest. Development of subaqueous levees tends to inhibit further increases in effluent expansion, so that with continuing bar accretion continuity can no longer be maintained simply by increasing effluent width. As the central part of the bar grows upward, channelization develops along the threads of maximum turbulence, which tend to follow the subaqueous levee. This process results in formation of a bifurcating channel, which has a triangular middle ground shoal separating diverging channel arms. This type of channel pattern is well displayed in the high-altitude photograph shown as [[:file:M31F16.jpg|Figure 1]].

[[file:M31F18.jpg|thumb|500px|{{figure number|3}}Cores of distributary-mouth bar sequence. Diameter of cores is 13 cm (5 in.). A. Smooth, gray, partially laminated clays of the prodelta deposits. B. Steeply dipping sand-silt laminations characteristic of block slumping often found in the prodelta environment. C. Small lenticular laminations and graded parallel silt laminations common near the top of the prodelta environment. D. Alternating sand, silt, and silty clay laminations in the lower part of the distal bar environment. E. Well-developed parallel silt and sand laminations showing graded bedding and small-scale ripple laminations common in the distal bar deposits. F. Lenticular sand laminations representing "starved current ripples" and small-scale ripple laminations common in the transition zone between the distal bar and distributary-mouth bar. G. Slump structure common near the shear plane in a distributary-mouth bar sequence that has mass-moved seaward. H. Cross laminations common in the distributary-mouth bar sands. The dark material is transported organic debris. I. Large-scale cross laminations common near the top part of the distributary-mouth bar deposits. The dark material is transported organic debris. J. Alternating silty sand and clay layers common to the small overbank splays that cap the distributary-mouth bar deposits.<ref name=Colemanetal_1981 />]]

[[file:M31F18.jpg|thumb|500px|{{figure number|3}}Cores of distributary-mouth bar sequence. Diameter of cores is 13 cm (5 in.). A. Smooth, gray, partially laminated clays of the prodelta deposits. B. Steeply dipping sand-silt laminations characteristic of block slumping often found in the prodelta environment. C. Small lenticular laminations and graded parallel silt laminations common near the top of the prodelta environment. D. Alternating sand, silt, and silty clay laminations in the lower part of the distal bar environment. E. Well-developed parallel silt and sand laminations showing graded bedding and small-scale ripple laminations common in the distal bar deposits. F. Lenticular sand laminations representing "starved current ripples" and small-scale ripple laminations common in the transition zone between the distal bar and distributary-mouth bar. G. Slump structure common near the shear plane in a distributary-mouth bar sequence that has mass-moved seaward. H. Cross laminations common in the distributary-mouth bar sands. The dark material is transported organic debris. I. Large-scale cross laminations common near the top part of the distributary-mouth bar deposits. The dark material is transported organic debris. J. Alternating silty sand and clay layers common to the small overbank splays that cap the distributary-mouth bar deposits.<ref name=Colemanetal_1981 />]]

Depositional areas are composed of several overlapping lobes owing to periodic discharge events, and each discharge is associated with its own distinctive nose. Seaward of the edge of the lobes, extensive small-scale pressure ridges are arranged sinuously and parallel. Extensive fields of mud vents and volcanoes emitting gas, water and fluid mud are found associated with the lobes and directly seaward of the noses; these undoubtedly result from rapid loading of underlying sediment as well as consolidation processes within the debris itself. Thicknesses of the lobes are difficult to determine, but each distinct lobe is normally 20 or so meters thick, and because of overlapping, the total thickness of mudflow can often approach 50 to 60 m. In one area of the Mississippi River delta, in water depths of approximately 200 to 250 m, depositional lobes cover approximately 770 sq km with discharged debris volume of 11.2 x 10⁶ cu m.

Depositional areas are composed of several overlapping lobes owing to periodic discharge events, and each discharge is associated with its own distinctive nose. Seaward of the edge of the lobes, extensive small-scale pressure ridges are arranged sinuously and parallel. Extensive fields of mud vents and volcanoes emitting gas, water and fluid mud are found associated with the lobes and directly seaward of the noses; these undoubtedly result from rapid loading of underlying sediment as well as consolidation processes within the debris itself. Thicknesses of the lobes are difficult to determine, but each distinct lobe is normally 20 or so meters thick, and because of overlapping, the total thickness of mudflow can often approach 50 to 60 m. In one area of the Mississippi River delta, in water depths of approximately 200 to 250 m, depositional lobes cover approximately 770 sq km with discharged debris volume of 11.2 x 10⁶ cu m.

A third major type of sediment instability of significant geological importance is arcuate rotational slump and growth fault. This type commonly occurs on the outer continental shelf in front of the advancing or prograding deltaic system. Large, arcuate-shaped families of shelf-edge slumps and deep-seated contemporaneous faults tend to be active along the peripheral margins of delta fronts. In most instances, these large-scale features tend to cut the modern sediment surface, often forming localized scarps on the seafloor. These surface scarps provide localized areas for accumulation of downslope mass-moved shallow-water sediment. In many places shelf-edge slumps tend to give a stairstepped appearance to the edge of the continental shelf and are highly reminiscent of rotational peripheral slumps higher on the continental shelf, near the mouths of the modern distributaries. However, these features generally occur on a much larger scale and cut a column of sediment ranging from 50 to 150 m in thickness.

A third major type of sediment instability of significant geological importance is arcuate rotational slump and [[growth fault]]. This type commonly occurs on the outer continental shelf in front of the advancing or prograding deltaic system. Large, arcuate-shaped families of shelf-edge slumps and deep-seated contemporaneous faults tend to be active along the peripheral margins of delta fronts. In most instances, these large-scale features tend to cut the modern sediment surface, often forming localized scarps on the seafloor. These surface scarps provide localized areas for accumulation of downslope mass-moved shallow-water sediment. In many places shelf-edge slumps tend to give a stairstepped appearance to the edge of the continental shelf and are highly reminiscent of rotational peripheral slumps higher on the continental shelf, near the mouths of the modern distributaries. However, these features generally occur on a much larger scale and cut a column of sediment ranging from 50 to 150 m in thickness.

Lateral continuities of individual slump scarps range from a few kilometers to as much as 8 to 10 km, and scarps on the seafloor produced by this slumping process may have heights of 30 m. A similar type of slump is commonly referred to as a contemporaneous or growth fault and is the feature moving continuously along the shear plane with deposition. Hence with time and continued movements, offsets of individual marker beds increase with depth, and thickness of these beds increases abruptly across the fault.

Lateral continuities of individual slump scarps range from a few kilometers to as much as 8 to 10 km, and scarps on the seafloor produced by this slumping process may have heights of 30 m. A similar type of slump is commonly referred to as a contemporaneous or growth fault and is the feature moving continuously along the shear plane with deposition. Hence with time and continued movements, offsets of individual marker beds increase with depth, and thickness of these beds increases abruptly across the fault.