方向を逆転させた河川のリスト

List of rivers that have reversed direction — Grokipedia Fact-checked by Grok 3 months ago List of rivers that have reversed direction Ara Eve Leo Sal 1x A list of rivers that have reversed direction encompasses waterways whose natural flow has shifted from the prevailing downstream gradient to an upstream or alternative path, either through permanent geological reconfiguration or transient disruptions. Such reversals typically arise from causal mechanisms rooted in physical processes, including tectonic uplift outpacing fluvial incision, leading to drainage piracy or basin capture; erosional headward migration breaching divides; or temporary blockages and hydraulic gradients from glacial advances, seismic liquefaction , or extreme precipitation events. [1] [2] Permanent reversals often reflect long-term tectonic dynamics, as seen in the ancient Amazon River , which drained westward toward the Pacific before Andean orogenesis elevated barriers, redirecting it eastward to the Atlantic around 10-23 million years ago. [3] Similarly, the Yangtze River's dramatic "First Bend" resulted from rapid uplift in the eastern Tibetan Plateau , inverting a southward flow to northward via capture of the former Shuiluo River during the late Cenozoic . [4] These cases illustrate how differential uplift and lithospheric deformation can fundamentally alter drainage networks over geological timescales, with empirical evidence from sediment provenance, paleocurrent indicators, and thermochronology confirming the shifts. [5] Temporary reversals, while rarer and shorter-lived, demonstrate rivers' sensitivity to acute perturbations; for instance, the Mississippi River flowed upstream for hours to days during the 1811-1812 New Madrid seismic sequence, as liquefaction and fault slip temporarily inverted local gradients, corroborated by contemporary observations and subsequent geomorphic scars. [6] In glaciated regions, the pre-glacial Wisconsin River reversed eastward when Laurentide ice lobes dammed its southern outlet, ponding waters that overflowed into the ancestral Michigan basin , as evidenced by inverted drainage remnants and LiDAR-mapped paleochannels. [7] Such events underscore the interplay of endogenic and exogenic forces, though claims of reversal must be vetted against potential exaggeration in anecdotal reports, prioritizing geophysical data over unsubstantiated narratives. [8] Mechanisms of Reversal Natural Mechanisms Tectonic uplift represents a primary natural mechanism for river reversal, occurring over geological timescales as plate interactions elevate terrain, thereby modifying drainage divides and basin gradients. When uplift creates barriers or tilts land surfaces, rivers may be forced to abandon prior paths in favor of newly lowered outlets, effectively reversing flow directions in affected segments. For example, Miocene uplift of the northern and central Andes , between approximately 16 and 11.5 million years ago, coupled with lithospheric processes, induced a major drainage reversal in the proto-Amazon system by blocking westward flow and redirecting it eastward toward the Atlantic Ocean. [9] [10] This process exemplifies how surface elevation changes, driven by subduction-related compression, can reorganize vast fluvial networks through first-principles of gravitational flow seeking minimal potential energy paths. Glacial isostatic adjustment, or post-glacial rebound , provides another mechanism, particularly in regions deglaciated after the Pleistocene. The removal of massive ice loads allows viscoelastic mantle flow to elevate the crust at rates up to several millimeters per year, altering local slopes and potentially inverting drainage directions where rebound gradients oppose prior flow. In northern North America , early Holocene river hydrology shifted due to such adjustments, with empirical evidence from stratigraphic records showing modified channel morphologies independent of climatic forcing alone. [11] This rebound, ongoing since the Last Glacial Maximum around 20,000 years ago, demonstrates causal links between isostatic recovery and fluvial reconfiguration via changes in hydraulic gradients. Erosional processes, including headward incision and avulsion, can precipitate reversals when rivers erode into adjacent basins, capturing and inverting tributaries through gradient advantages. Avulsion occurs when overbank deposition raises floodplain elevations, prompting sudden shifts to steeper, unincised channels that may redirect flow oppositely if the new path aligns with broader topographic lows. Geological reconstructions, supported by sediment core analyses revealing shifts in depositional provenance , confirm such erosional captures in ancient systems like pre-Holocene Mississippi channels, where differential incision overcame prior alignments. [12] Catastrophic geomorphic events, such as landslides or seismic activity, induce rapid reversals by damming valleys and forcing overflow into upstream or lateral courses; permanence arises if dams endure without breaching, stabilizing the altered hydrology . Earthquakes generate coseismic river responses, including landslide blockages that reroute flow, with sedimentological evidence indicating occasional long-term shifts where new channels entrench before dam failure . [13] [14] These mechanisms underscore the interplay of mass wasting and tectonic instability in transiently or durably reversing fluvial dynamics. Anthropogenic Mechanisms Human-induced river reversals primarily occur through engineered alterations to the hydraulic gradient , where infrastructure redirects flow from the original downstream path to an alternative lower outlet, often for sanitation , navigation , or water management purposes. The core principle involves excavating channels or canals that bypass natural divides, creating an artificial slope that inverts the river's direction relative to its topographic base level. This is achieved by ensuring the engineered outlet maintains a lower elevation or hydraulic head than the source, sometimes augmented by diverting additional water volumes to overcome natural inertia and friction losses in the channel. [15] [16] The most prominent example is the Chicago River in Illinois, United States, whose main stem and South Branch were reversed on January 1, 1900, via the 28-mile (45 km) Chicago Sanitary and Ship Canal. Prior to reversal, the river discharged into Lake Michigan, risking contamination of the city's drinking water supply by upstream sewage during heavy rains or low lake levels. Engineers addressed this by connecting the South Branch to the Des Plaines River—a tributary of the Mississippi River watershed—through a canal excavated with a gentle gradient of approximately 1 foot per mile (0.3 m/km) toward the southwest. This inverted the flow by leveraging the continental divide's subtle elevation difference (about 3 feet or 0.9 m higher on the Lake Michigan side), while locks and dams controlled water levels to prevent backflow from the Mississippi and maintain the reversal. To sustain the inverted direction, the system relies on continuous diversion of Lake Michigan water—up to 3,000 cubic feet per second (85 m³/s) under normal conditions—exceeding natural watershed inflows and generating sufficient momentum to propel effluent westward. [17] [18] [15] Dam and reservoir systems can contribute to reversals by manipulating upstream water levels to create backwater effects that overpower natural downstream gradients, particularly in interconnected river networks for flood control or hydropower generation. For instance, large reservoirs may elevate tailwater to reverse local tributaries or branches, though full main-stem reversals require coordinated multi-dam operations to sustain the altered head difference. Such mechanisms depend on precise regulation of spillway discharges and storage capacities to ensure the reservoir outflow exceeds inflow in the reversed segment, often verified through post-construction gauging data showing sustained velocity shifts. [19] Urban modifications, including dredging and channel realignment, support reversals by reducing bed friction and optimizing cross-sections to enhance flow efficiency in the new direction, typically integrated with canals or weirs. In the River Spree near Berlin , Germany , sectional reversals in urban reaches result from weirs and interbasin connections that divert higher-volume inflows from adjacent rivers like the Havel , inverting local gradients through controlled hydraulic structures rather than natural topography . These interventions require ongoing sediment management and structural maintenance to counteract erosion or sedimentation that could restore original flows, with hydrological monitoring confirming directional stability via current meters and stage records. [20] [19] Permanent Reversals Geological Permanent Reversals The Amazon River represents a classic case of permanent drainage reversal driven by tectonic uplift. Prior to the late Miocene , approximately 11.8 to 8.3 million years ago, the proto-Amazon drained westward toward the Pacific Ocean , as indicated by paleocurrent indicators and sediment provenance in Andean foreland basins. The progressive uplift of the Andes Mountains, resulting from subduction-related tectonics , impounded the western drainage, forcing a reversal to eastward flow into the Atlantic Ocean; this shift is evidenced by the abrupt onset of deep-sea fan deposition in the Foz do Amazonas Basin and geochemical signatures of Andean-derived sediments reaching the Atlantic margin thereafter. [21] [9] Segments of the ancient Mississippi River system experienced multiple flow reversals during the Pleistocene epoch, primarily due to glacial loading and unloading that induced crustal tilting and deltaic progradation. Stratigraphic cores from the Gulf Coast reveal episodic diversions and back-tilting of channels, with pre-Illinoian segments initially