Collapse Of Delta Research Articles

Lacustrine mass movements in active tectonic settings: Lake tsunami sources in New Zealand's South Island

Lake tsunamis generated from subaerial and subaqueous mass movements can pose a significant hazard to lakeshore communities. However, current knowledge of lake tsunamis is derived from a limited number of studies, primarily in low-seismicity settings such as Switzerland and Norway. Underrepresented are studies from active tectonic settings, characterised by high relief, high sediment yields, and frequent seismic shaking that is likely to produce episodic subaerial and subaqueous mass movements with the potential to produce lake tsunamis. This study seeks to address this gap in our understanding through an examination of four lakes in the active tectonic region of New Zealand's South Island (Lake Rotoiti, Lake Rotoroa, Lake Brunner, and Lake Mapourika). High-resolution multibeam bathymetry and high-resolution seismic reflection data were used to identify and characterize the landforms and sediment associations of large and potentially tsunamigenic mass movements. A qualitative evaluation of the tsunamigenic capacity of the identified mass movements was undertaken using established empirical relationships between mass movement volumes and run-up heights. The bathymetric and seismic surveys have revealed 16 previously undocumented mass movements capable of generating lake tsunami. Fluvial deltas and bedrock slopes proximal to active faults were the most prevalent mass movement source areas, with the largest mass movements identified being a 49 Mm3 delta collapse and a 110 Mm3 subaerial mass movement in Lake Rotoroa. The findings suggest the origin and characteristics of the potentially tsunamigenic mass movements identified were strongly influenced by the high rates of delta progradation, frequent seismic activity, and the preconditioning and displacement by active faults, typical of active tectonic settings. Our results provide new insights into the heterogeneity of lacustrine mass movements and the drivers of lake tsunami hazards in underrepresented high-seismicity regions. The findings illustrate the importance of developing regionally specific insights into lake tsunami susceptibility and may inform the direction of more detailed lake tsunami hazard assessment in New Zealand.

Lacustrine evidence reveals spatially and temporally distinct Holocene ruptures on the Sawtooth Fault, Central Idaho, USA

ABSTRACTThe Sawtooth Fault in central Idaho, USA, is a range‐bounding normal fault with a Late Pleistocene–Holocene scarp near the up‐valley ends of several range‐front lakes. Cores from Redfish Lake, which spans the fault, exhibit evidence of catastrophic sediment re‐mobilization in two sequences consisting variably of intraclastic mud‐clast conglomerate, massive homogenite, and graded silt and clay. Event strata of the younger sequence are in unconformable contact with Pleistocene sediments in two cores on the northern lake‐basin slope, suggesting transport from the down‐valley portion of the lake toward the basin center. A silt cap associated with the event strata is preserved at all coring sites. The event sequence, distributed lake‐wide, dates to ca. 4300 cal a bp, while additional event strata in two Redfish Lake cores pre‐date the 7627 cal a bp Mazama ash. We propose seismic triggering of the sediment disruptions. Asynchronous event stratigraphy in Pettit Lake, 15 km south of Redfish Lake, suggests distinct ruptures along two portions of the Sawtooth Fault. The sedimentology and geochemistry of remobilized sediments in both lakes indicates that sources included Late Pleistocene and early Holocene lake‐floor sediments and suggests failures that cut deeply into the sedimentary sequence. Cores collected from Stanley Lake (17 km northwest of Redfish Lake) following the nearby 2020 M6.5 Stanley earthquake exhibit a thin, sandy event horizon associated with documented delta collapse. Subaerial slope failures associated with the 2020 event left no widespread disturbance stratigraphy in Redfish Lake. We conclude that the large‐magnitude lake‐floor sediment remobilization events probably required rupture of fault sections proximal to Redfish and Pettit lakes.

New insights on the gravity-driven deformation of late Albian – early Turonian stacked delta collapse systems in the Ceduna sub-basin, Bight Basin, southern margin of Australia

Gravitational collapse of delta systems is thin-skinned deformation due to sedimentary loading that induces spreading or sliding above a very weak detachment layer and typically consists of up-dip listric extensional faults linked to down-dip a compressional system of toe-thrusts. Detailed mapping and analysis of a modern high-quality, 3D depth-migrated seismic data set from the offshore Ceduna sub-basin, southern Australian margin has shown that gravitational collapse in this sub-basin occurred by multiple failure episodes. We show that the late Albian – early Turonian succession consists of two stacked collapse features; a previously unrecognised Albian–early Cenomanian system 1 and the overlying system 2 of the Cenomanian–early Turonian White Pointer delta of the Ceduna sub-basin.Collapse system 1 is located beneath the extensional domain of the Cenomanian – early Turonian White Pointer collapse system 2, which itself consists of three structural sub-domains that are classified based on fault architectures and geometries, and are named after their relative location as proximal, central, and distal sub-domain. Individual sub-domain consists of scoop-shaped listric normal faults linked downwards to thrust faults. The main faults of these sub-domains detach on multiple decollement surfaces of shales, presumably overpressured. This study proposes an investigation into the development of stacked and complex basinwards sequential formation of gravity collapse features in delta systems on passive margins. The research documents the complex structural styles and evolution of the late Albian – early Turonian stacked delta collapse systems and proposes a revised structural and stratigraphic framework of the Ceduna sub-basin. A four-dimensional (4D) tectonostratigraphic models for the evolution of the late Albian – early Turonian succession within the Ceduna sub-basin is also proposed.

A tsunamigenic delta collapse and its associated tsunami deposits in and around Lake Sils, Switzerland

Large lacustrine mass movements and delta collapses are increasingly being considered as potential tsunamigenic sources and therefore hazardous for the population and infrastructure along lakeshores. Although historical reports document tsunami events in several lakes in Switzerland, and although the propagation of lake tsunamis has been studied by numerical wave modeling, only little is known about on- and offshore lacustrine tsunami deposits. In Lake Sils, Switzerland, a large prehistoric mass-movement deposit originating from the Isola Delta with a minimum estimated volume of 6.5 × 106 m3 and a basinal thickness of > 6 m in the seismic record has been identified by previous studies and radiocarbon dated to around 700 Common Era. Here, we combine (i) comprehensive sedimentological investigation of sediment cores recovered from the on- and offshore settings, (ii) mineralogical fingerprinting of the inflows from key catchments to characterize sediment provenance, and (iii) numerical tsunami modeling, to test the hypothesis of a tsunamigenic delta collapse in Lake Sils. We observe a clastic event deposit consisting of coarse-grained, fining-upward sand overlying an organic-rich peat deposit in the shallow water. This layer thins and fines landward on the coastal plain. Toward the deeper water (20–40 m), the deposit transforms into a thicker and more heterogeneous sediment package with multiple sequences of fining-upward sand and a well-pronounced clay cap at the top. Radiocarbon dating of the peat underlying the event deposit yields a maximum age of 225–419 calibrated Common Era. The tsunami models, which indicate wave heights reaching up to 5 m, simulate areas of inundation that coincide with the location of event deposits. Based on our results, we propose that the historically undocumented Isola Delta collapse generated a basin-wide tsunami that inundated the lakeshore, transporting large amounts of unconsolidated sediment along the lakeshore toward the coastal plain and into the deeper lake basin.

Growth‐faults from delta collapse – structural and sedimentological investigation of the Last Chance delta, Ferron Sandstone, Utah

AbstractInvestigations of syn‐sedimentary growth faults in the Last Chance delta (Ferron Sandstone, Utah, USA) show that fault‐bounded half‐grabens arrested high amounts of sand in the mouth bar and/or distributary channel areas. Fault‐controlled morphology causes changes in routing of the delta top to delta front drainage towards the long axis of half‐grabens. Faulting was spatially and temporally non‐systematic, and polyphase, with 3D cusp/listric fault geometries instigated by linkage of variously oriented segments. Hanging wall rollover folds consisting of wedge‐shaped syn‐kinematic sand attest to rapid <1‐m slip increments on faults followed by mild erosion along crests of fault blocks and sedimentary infill of adjacent accommodation. Triangle‐zones in prodelta to delta front muds are located underneath steeper faults and interconnected rotated fault‐flats. Their geometry is that of antiformal stack duplexes, in an arrangement of low‐angle‐to‐bedding normal faults at the base, replaced by folded thrusts upwards. These faults show a brittle, frictional flow deformation mechanism ascribed to early compaction of mud. For syn‐kinematic sand, there is a change from general granular/hydroplastic flow in shear zones to later brittle failure and cataclasis, a transition instigated by precipitation of calcite cement. Extensional faulting in the Last Chance delta was likely controlled by gravity driven collapse towards the delta slope and prodelta, as is commonly observed in collapsing deltas. The trigger and driving mechanism is envisioned as localized loads from sand deposited within distributary channels/mouth bars and fault‐controlled basins along the delta top. A regional tilt and especially displacement of compacted mud below sand bodies towards less compacted muds also contributed to the faulting.

Asymmetric Effects of Subaerial and Subaqueous Basement Slopes on Self‐Similar Morphology of Prograding Deltas

AbstractDeltas form over basements of various slope configurations. While the morphodynamics of prograding deltas over single‐slope basements have been studied previously, our understanding of delta progradation over segmented basements is still limited. Here we use experimental and analytical approaches to investigate the deltaic morphologies developing over two‐slope basements with unequal subaerial and subaqueous slopes. For each case considered, the scaled profiles of the evolving delta collapse to a single profile for constant water and sediment influxes, allowing us to use the analytical self‐similar profiles to investigate the individual effects of subaerial/subaqueous slopes. Individually varying the subaerial/subaqueous slopes exerts asymmetric effects on the morphologies. Increasing the subaerial slope advances the entire delta; increasing the subaqueous slope advances the upstream boundary of the topset yet causes the downstream boundary to retreat. The delta front exhibits a first‐retreat‐then‐advance migrating trend with increasing subaqueous slope. A decrease in subaerial topset length is always accompanied by an increase in subaqueous volume fraction, no matter which segment is steepened. Applications are presented for estimating shoreline retreat caused by steepening of basement slopes, and estimating subaqueous volume and delta front using the observed topset length. The results may have implications for real‐world delta systems subjected to upstream tectonic uplift and/or downstream subsidence. Both scenarios would exhibit reduced topset lengths, which are indicative of the accompanied increases in subaqueous volume and signal tectonic uplift and/or subsidence that are at play. We highlight herein the importance of geometric controls on partitioning of sediment between subaerial and subaqueous delta components.

A comparison of the sedimentary records of the 1960 and 2010 great Chilean earthquakes in 17 lakes: Implications for quantitative lacustrine palaeoseismology

AbstractSeismically‐induced event deposits embedded in the sedimentary infill of lacustrine basins are highly useful for palaeoseismic reconstructions. Recent, well‐documented, great megathrust earthquakes provide an ideal opportunity to calibrate seismically‐induced event deposits for lakes with different characteristics and located in different settings. This study used 107 short sediment cores to investigate the sedimentary impact of the 1960 Mw 9·5 Valdivia and the 2010 Mw 8·8 Maule earthquakes in 17 lakes in South‐Central Chile (i.e. lakes Negra, Lo Encañado, Aculeo, Vichuquén, Laja, Villarrica, Calafquén, Pullinque, Pellaifa, Panguipulli, Neltume, Riñihue, Ranco, Maihue, Puyehue, Rupanco and Llanquihue). A combination of image analysis, magnetic susceptibility and grain‐size analysis allows identification of five types of seismically‐induced event deposits: (i) mass‐transport deposits; (ii) in situ deformations; (iii) lacustrine turbidites with a composition similar to the hemipelagic background sediments (lacustrine turbidites type 1); (iv) lacustrine turbidites with a composition different from the background sediments (lacustrine turbidites type 2) and (v) megaturbidites. These seismically‐induced event deposits were compared to local seismic intensities of the causative earthquakes, eyewitness reports, post‐earthquake observations, and vegetation and geomorphology of the catchment and the lake. Megaturbidites occur where lake seiches took place. Lacustrine turbidites type 2 can be the result of: (i) local near‐shore mass wasting; (ii) delta collapse; (iii) onshore landslides; (iv) debris flows or mudflows; or (v) fluvial reworking of landslide debris. On the contrary, lacustrine turbidites type 1 are the result of shallow mass wasting on sublacustrine slopes covered by hemipelagic sediments. Due to their more constrained origin, lacustrine turbidites type 1 are the most reliable type of seismically‐induced event deposits in quantitative palaeoseismology, because they are almost exclusively triggered by earthquake shaking. Moreover, they most sensitively record varying seismic shaking intensities. The number of lacustrine turbidites type 1 linearly increases with increasing seismic intensity, starting with no lacustrine turbidites type 1 at intensities between V½ and VI and reaching 100% when intensities are higher than VII½. Combining different types of seismically‐induced event deposits allows the reconstruction of the complete impact of an earthquake.

Identifying hazards associated with lava deltas

Lava deltas, formed where lava enters the ocean and builds a shelf of new land extending from the coastline, represent a significant local hazard, especially on populated ocean island volcanoes. Such structures are unstable and prone to collapse—events that are often accompanied by small explosions that can deposit boulders and cobbles hundreds of meters inland. Explosions that coincide with collapses of the East Lae ‘Apuki lava delta at Kīlauea Volcano, Hawai‘i, during 2005–2007 followed an evolutionary progression mirroring that of the delta itself. A collapse that occurred when the lava–ocean entry was active was associated with a blast of lithic blocks and dispersal of spatter and fine, glassy tephra. Shortly after delta growth ceased, a collapse exposed hot rock to cold ocean water, resulting in an explosion composed entirely of lithic blocks and lapilli. Further collapse of the delta after several months of inactivity, by which time it had cooled significantly, resulted in no recognizable explosion deposit. Seaward displacement and subsidence of the coastline immediately inland of the delta was measured by both satellite and ground-based sensors and occurred at rates of several centimeters per month even after the lava–ocean entry had ceased. The anomalous deformation ended only after complete collapse of the delta. Monitoring of ground deformation may therefore provide an indication of the potential for delta collapse, while the hazard associated with collapse can be inferred from the level of activity, or the time since the last activity, on the delta.

A Model for Cutting and Healing of Deltaic Mouth Bars At the Shelf Edge: Mechanism for Basin-Margin Accretion

Abstract The architecture and facies variability of shelf-edge deltaic deposits from Permian–Triassic strata of the Karoo Basin, South Africa, are described. The architecture of the deposits are used to propose a model of repetitive collapse and re-establishment of mouth-bar packages at the shelf edge, and associated delivery of sand to the slope and basin floor. Accretion of basin-margin sediment wedges is facilitated through deposition of sediment on the basin-margin clinoform. This sediment is delivered by deltas at the shelf edge in the form of turbidity currents, delta collapse, and other gravity-driven processes. A well exposed 3-km-long transect that records the transition between the outer shelf and upper slope for one progradational unit is described. The strata are defined by basinward-dipping, offlapping clinoform packages of soft-sediment-deformed and undeformed sandstone and mudstone. Undeformed sandstone units are characterized by meter-thick beds of mouth-bar sandstones with internal scour incisions, 1–2 m deep. Sets of undeformed sandstone beds thicken in a basinward direction from less than 1 m to over 10 m, and in multiple locations the bed sets are truncated by slump-scar surfaces that are overlain by mass-transport deposits. Soft-sediment-deformed strata are defined by packages of contorted, broken, and overturned beds. The deformed deposits are interpreted as being the product of dewatering features, as well as slumps, slides, and debrites, all of which emanate from slump-scar features at the shelf edge. On the uppermost slope, thin-bedded prodelta turbidites are interbedded with mass transport deposits, most of which pinch out within 2 km of the shelf edge. The clinoformal packages presented record the basinward transition between: a) prograding mouth-bar deposits on the delta topset, b) truncation of the mouth-bar deposits by slump-scar incisions, 2–6 m deep, c) deposition of mass-transport deposits on the delta front and prodelta, and finally, d) re-establishment of mouth-bar deposition above and basinward of the slump-scar and mass-transport deposits. The observed stratigraphic stacking patterns, facies transitions, and interpreted depositional systems form the basis of a model for cutting and healing of deltaic packages that describes the repetitive deltaic progradation, delta collapse, and subsequent re-establishment of deltaic deposition. This process of repetitive collapse and reestablishment records the depositional-element-scale progradation of the shelf edge and accretion of the basin margin within the same depositional sequence.

Architecture and sedimentology of the Kerinitis Gilbert-type fan delta, Corinth Rift, Greece

The Kerinitis Delta in the Corinth Rift, Greece, is a footwall derived, coarse-grained, Gilbert-type fan delta deposited in the hangingwall of a linked normal fault system. This giant Gilbert-type delta (radius 3-8 km, thickness > 600 m) was supplied by an antecedent river and built into a brackish to marine basin. Although as yet poorly dated, correlation with neighbouring deltas suggests that the Kerinitis Delta was deposited during a period of 500 to 800 ka in the Early to early Middle Pleistocene. Facies characterizing a range of depositional processes are assigned to four facies associations (topset, foreset, bottomset and prodelta). The dominantly fluvial topset facies association has locally developed shallow marine (limestone) and fluvial-shoreface sub-associations. This delta represents a subsidence-dominated system in which high fault displacement overwhelmed base-level falls (creation of accommodation predominantly > 0). Stratal geometries and facies stacking patterns were used to identify 11 key stratal surfaces separating 11 stratal units. Each key stratal surface records a landward shift in the topset breakpoint path, indicating a rapid increase in accommodation/sediment supply. Each stratal unit records a gradual decrease in accommodation/sediment supply during deposition. The cyclic stratal units and key stratal surfaces are interpreted as recording eustatic falls and rises, respectively. A 30 m thick package of foresets below the main delta records the nucleation of a small Proto-delta probably on an early relay ramp. Based on changes in stratal unit geometries, the main delta is divided into three packages, interpreted as recording the initiation, growth and death of the controlling fault system. The Lower delta comprises stacked, relatively thin, progradational stratal units recording low displacement on the young fault system (relay ramp). The Middle delta comprises vertically stacked stratal units each recording initial aggradation–progradation followed by progradation; their aggradational component increases up through the Middle delta, which records the main phase of increasing rate of fault displacement. The Upper delta records pure progradation, recording abrupt cessation of movement on the fault. A major erosion surface incising basinward 120 m through the Lower and Middle delta records an exceptional submarine erosion process (canyon or delta collapse).

The 1996 AD delta collapse and large turbidite in Lake Brienz

In spring 1996 AD, the occurrence of a large mass-transport was detected by a series of events, which happened in Lake Brienz, Switzerland: turbidity increase and oxygen depletion in deep waters, release of an old corpse into surface waters and occurrence of a small tsunami-like wave. This mass-transport generated a large turbidite deposit, which is studied here by combining high-resolution seismic and sedimentary cores. This turbidite deposit correlates to a prominent onlapping unit in the seismic record. Attaining a maximum of 90 cm in thickness, it is longitudinally graded and thins out towards the end of the lake basin. Thickness distribution map shows that the turbidite extends over ∼ 8.5 km 2 and has a total volume of 2.72 ⁎ 10 6 m 3, which amounts to ∼ 8.7 yr of the lake's annual sediment input. It consists of normally graded sand to silt-sized sediment containing clasts of hemipelagic sediments, topped by a thin, white, clay-sized layer. The source area, the exact dating and the possible trigger of this turbidite deposit, as well as its flow mechanism and ecological impact are presented along with environmental data (river inflow, wind and lake-level measurements). The combined results indicate that no particular cause (i.e., earthquake, explosion, flood, wind storm, lake-level change, seiche or sediment dredging) triggered the 1996 AD large turbidite deposit. Instead, it was due to a delta slope failure most likely caused by normal sediment accumulation.

Mitochondria in Ca2+ signaling and apoptosis.

Cellular Ca2+ signals are crucial in the control of most physiological processes, cell injury and programmed cell death; mitochondria play a pivotal role in the regulation of such cytosolic Ca2+ ([Ca2+]c) signals. Mitochondria are endowed with multiple Ca2+ transport mechanisms by which they take up and release Ca2+ across their inner membrane. These transport processes function to regulate local and global [Ca2+]c, thereby regulating a number of Ca2+-sensitive cellular mechanisms. The permeability transition pore (PTP) forms the major Ca2+ efflux pathway from mitochondria. In addition, Ca2+ efflux from the mitochondrial matrix occurs by the reversal of the uniporter and through the inner membrane Na+/Ca2+ exchanger. During cellular Ca2+ overload, mitochondria take up [Ca2+]c, which, in turn, induces opening of PTP, disruption of mitochondrial membrane potential (delta(psi)m) and cell death. In apoptosis signaling, collapse of delta(psi)m and cytochrome c release from mitochondria occur followed by activation of caspases, DNA fragmentation, and cell death. Translocation of Bax, an apoptotic signaling protein from the cytosol to the mitochondrial membrane, is another step during this apoptosis-signaling pathway. The role of permeability transition in the context of cell death in relation to Bcl-2 family of proteins is discussed.

Littoral hydrovolcanic explosions: a case study of lava–seawater interaction at Kilauea Volcano

A variety of hydrovolcanic explosions may occur as basaltic lava flows into the ocean. Observations and measurements were made during a two-year span of unusually explosive littoral activity as tube-fed pahoehoe from Kilauea Volcano inundated the southeast coastline of the island of Hawai`i. Our observations suggest that explosive interactions require high entrance fluxes (≥4 m 3/s) and are most often initiated by collapse of a developing lava delta. Two types of interactions were observed. “Open mixing” of lava and seawater occurred when delta collapse exposed the mouth of a severed lava tube or incandescent fault scarp to wave action. The ensuing explosions produced unconsolidated deposits of glassy lava fragments or lithic debris. Interactions under “confined mixing” conditions occurred when a lava tube situated at or below sea level fractured. Explosions ruptured the roof of the tube and produced circular mounds of welded spatter. We estimate a water/rock mass ratio of 0.15 for the most common type of littoral explosion and a kinetic energy release of 0.07–1.3 kJ/kg for the range of events witnessed.