Shoreline Terraces Research Articles

The role of geomorphology in the Quaternary

Abstract The advances in understanding of Quaternary geomorphology in the latter half of the twentieth century were closely linked with the improved knowledge of Quaternary climatic fluctuation, principally derived from isotopic evidence from ocean and ice cores. An important goal was finding terrestrial sedimentary records that can be correlated with the globally applicable isotopic sequence. From a geomorphological viewpoint, river terraces are paramount, particularly since they can provide semi-continuous sequences that record palaeoclimate and landscape evolution throughout the Quaternary, as well as the interaction of rivers with glaciation, sea-level change and notable geomorphological events. In coastal areas, shoreline terraces and raised beaches can provide similar sequences. The chapter discusses the progress made in understanding these archives and, in particular, the various mechanisms for dating and correlation, as well as touching upon contributions from other environments, namely slopes and karstic systems, as well as the role of soils in deciphering geomorphological evidence.

Kelp DNA records late Holocene paleoseismic uplift of coastline, southeastern New Zealand

Holocene paleoseismic activity on the Akatore Fault zone, southeastern New Zealand, has caused uplift of a 23 km section of coastline by several metres. Prominent relict shoreline terraces are preserved at 6 m and 3 m above the present sea level, and the latter terrace was formed 1000-1400 yrs BP. The main fault strand farther inland has 6 m of late Holocene vertical offset, but the relationships between coastal offsets and fault offsets are not understood. There is no preserved geological evidence on the coastline to distinguish between incremental uplift (e.g., numerous centimetre-scale events) and major, metre-scale, uplift events: a distinction that is important for evaluating regional paleoseismicity. We have used genetic characterisation of populations of live kelp, Durvillaea antarctica growing along the shoreline to investigate whether or not there has been a catastrophic uplift event, greater than the two metre tidal range, that was sufficient to extirpate intertidal kelp populations. Our results show that all kelp along the southeastern New Zealand coastline belongs to the same distinctive clade of D. antarctica, and inhabits the same ecological niches on exposed rocks and reefs. However, the kelp population on the uplifted coastline is genetically uniform, and clearly distinct from those of flanking shorelines. This regional genetic anomaly is consistent with a major extirpation event, followed by recolonisation from source populations some 30-120 km to the northeast of the uplifted coast. The uplift event caused vertical crustal movement with similar amounts of uplift on the fault plane and the coastline 3 km away. This approach, using genetics of intertidal biota, has potential applications for evaluation of paleoseismicity of other tectonically active shorelines around the world.

Evidence for multiple Plio-Pleistocene lake episodes in the hyperarid Atacama Desert

Abstract Cosmogenic nuclide exposure dating of ancient shoreline terraces of the Quillagua-Llamara Soledad Lake in the central Atacama Desert of northern Chile provides new insights in the paleohydrology of the driest desert on Earth. The lake developed in a paleo-endorheic drainage system in the Central Depression prior to draining into the Pacific due to incision of the Rio Loa canyon. The durations of lake stages were sufficiently long to form wave-erosion induced shoreline terraces on the wind-exposed slopes of former islands. Successively younger shoreline levels are preserved over an elevation range of 250 m due to progressive uplift of the islands coeval with the lake stages. Cosmogenic 10Be- and 21Ne-derived exposure ages of the shorelines reveals that the hyperarid conditions in the Rio Loa catchment were interspersed by several pluvial stages during the Pliocene and Pleistocene, which generated a large and persistent lake in the Quillagua-Llamara basin. The exposure ages of the final lake stage provide the maximum age for the incision of the Rio Loa canyon (274 ± 74 ka) and the subsequent breaching of the Coastal Cordillera.

Assessing the relevance of littoral pedestals to chlorophyll a levels in a shallow lentic freshwater system

AbstractPedestals or shoreline terraces, a disjuncture of the last flooding level with the adjacent littoral upland, can help in understanding the contribution of the shoreline to the productivity of the pelagic zones. We investigated littoral pedestal dynamics and assessed their ecological relevance to a water body, Manjirenji Dam in Zimbabwe, with marked and sharp drawdowns, in ten littoral sites by measuring chlorophyll a, water transparency, pedestal contour length and drawdown zone length once per month from August 2013 to April 2014. Chlorophyll a levels were not significantly correlated to the euphotic depth, pedestal contour length and the drawdown zone retraction length in Manjirenji Dam. Our results which are inconsistent with the hypothesis that drawdown zone and contour pedestal lengths are vital in predicting chlorophyll a concentration in the littoral zones of limnetic systems, suggest a need to explore other intricate limnological factors which may influence productivity in shallow reservoirs.

Monitoring geomorphologic changes using Landsat TM and ETM+ data in the Hendijan River delta, southwest Iran

Beach and delta areas are dynamic physical features with changes occurring at many spatial and temporal scales due to both general and catastrophic events. Geomorphic changes such as temporal and periodic changes in riverbeds and coasts are common events in all deltaic areas. The Hendijan river basin is located in the southwest of Iran, close to the city of the Hendijan and many villages and rural settlements. Changes in various geomorphic features, such as riverbed and shoreline migration, Sebkhas, alluvial terraces, meanders and old, dry rivers over 48 years of time, were detected and identified using Landsat TM and ETM satellite data and topographic maps. Simple bands subtraction, principal component analysis (PCA) and fuzzy logic were used to identify regions that have undergone land cover change. Results of this study show that the Hendijan River channel has migrated several times over the last 48 years. Several meanders and ox‐bow lakes remain as a result of migration. The shoreline has migrated over 4 km into the Persian Gulf. The resulting maps can be used in an integrated coastal zone information system as it has been proposed for the Heddijan delta.

60 k.y. record of extension across the western boundary of the Basin and Range province: Estimate of slip rates from offset shoreline terraces and a catastrophic slide beneath Lake Tahoe: Comment and Reply: REPLY

We welcome the opportunity to address the issues raised by Schweickert and Lahren in their Comment, which claims, among other charges, that we are guilty of flawed procedures and conceptual errors. It should be emphasized from the outset that we have employed a conservative approach in estimating

60 k.y. record of extension across the western boundary of the Basin and Range province: Estimate of slip rates from offset shoreline terraces and a catastrophic slide beneath Lake Tahoe: Comment and Reply: COMMENT

[Kent et al.'s (2005)][1] article, which claims a 60 k.y. record of extension and slip rates across the western boundary of the Basin and Range province, fails to deliver on its promises because of conceptual errors, flawed procedures, omissions, and other problems. The basic premise of the paper,

60 k.y. record of extension across the western boundary of the Basin and Range province: Estimate of slip rates from offset shoreline terraces and a catastrophic slide beneath Lake Tahoe

Deformation across three major fault strands within the Lake Tahoe basin has been mapped by using a novel combination of high-resolution seismic chirp, airborne laser- and acoustic-multibeam-derived bathymetry, and deep- and shallow-water sediment cores. Submerged erosional terraces of late Pleistocene age (19.2 6 1.8 ka) record vertical de- formation across fault strands that ranges between 10 and 15 m; offset of 10 m is observed across the southern part of the West Tahoe fault. Avalanche deposits from the catastrophic McKinney Bay slide (ca. 60 ka) are offset across the Stateline fault by at least 21-25 m. The submerged shoreline terraces and debris avalanche provide marker beds with which to constrain the extensional history of the region for the past 60 k.y. This history is then used to assess the future seismic hazard of the region. Data on deformation across these two important marker beds, combined with chronological control from 14 C and optically stimulated luminescence measurements, yield an estimate of extension across the Lake Tahoe basin that is 0.4-0.5 mm/yr. On the basis of these measurements, there exists the potential for a large, seiche wave-generating M7 earthquake every ;3 k.y. Late Pleisto- cene and Holocene vertical deformation rates within the Tahoe basin are characteristic of Basin and Range faulting and place the Tahoe basin within the western limits of the extensional Basin and Range province.

Hydrothermal and tectonic activity in northern Yellowstone Lake, Wyoming

Yellowstone National Park is the site of one of the world9s largest calderas. The abundance of geothermal and tectonic activity in and around the caldera, including historic uplift and subsidence, makes it necessary to understand active geologic processes and their associated hazards. To that end, we here use an extensive grid of high-resolution seismic reflection profiles (∼450 km) to document hydrothermal and tectonic features and deposits in northern Yellowstone Lake. Sublacustrine geothermal features in northern Yellowstone Lake include two of the largest known hydrothermal explosion craters, Mary Bay and Elliott9s. Mary Bay explosion breccia is distributed uniformly around the crater, whereas Elliott9s crater breccia has an asymmetric distribution and forms a distinctive, ∼2-km-long, hummocky lobe on the lake floor. Hydrothermal vents and low-relief domes are abundant on the lake floor; their greatest abundance is in and near explosion craters and along linear fissures. Domed areas on the lake floor that are relatively unbreached (by vents) are considered the most likely sites of future large hydrothermal explosions. Four submerged shoreline terraces along the margins of northern Yellowstone Lake add to the Holocene record of postglacial lake-level fluctuations attributed to “heavy breathing” of the Yellowstone magma reservoir and associated geothermal system. The Lake Hotel fault cuts through northwestern Yellowstone Lake and represents part of a 25-km-long distributed extensional deformation zone. Three postglacial ruptures indicate a slip rate of ∼0.27 to 0.34 mm/yr. The largest (3.0 m slip) and most recent event occurred in the past ∼2100 yr. Although high heat flow in the crust limits the rupture area of this fault zone, future earthquakes of magnitude ∼5.3 to 6.5 are possible. Earthquakes and hydrothermal explosions have probably triggered landslides, common features around the lake margins. Few high-resolution seismic reflection surveys have been conducted in lakes in active volcanic areas. Our data reveal active geothermal features with unprecedented resolution and provide important analogues for recognition of comparable features and potential hazards in other subaqueous geothermal environments.

Quantitative characterization and elevation estimation of Lake Lahontan shoreline terraces from high‐resolution digital elevation models

The precision with which the elevation of a feature, such as a terrace, can be measured depends on the characterization of the noise contaminating the measurement. A method for identification and extraction of terrace feature elevations is presented and the topographic noise, due to erosion, as well as measurement error, is quantified. High‐resolution digital elevation models (DEM) are acquired at six wave‐cut, volcanic bedrock terrace sites from around the highstand of paleo‐Lake Lahontan in the western Great Basin. Local DEMs, which are tied to regional geodetic control, were acquired using conventional total station, rapid postprocessed and real‐time kinematic Global Positioning System methods. The topographic signal is processed with derivative filters for geomorphic feature recognition and averaging for noise reduction. Results indicate that noise levels for identifiable features such as riser crest, knickpoint, and slope inflection point are statistically equivalent and on the order of 0.5 m standard deviation. Averaging within topographic bins spanning ∼50 m along terrace strike yields feature elevation estimates with standard errors on the order of 0.12 m. The mean bench window elevation (between the riser crest and knickpoint) has the lowest standard error and is systematically related to water level. Propagation of surveying, geoid estimation, and terrace feature elevation estimation errors indicates that displacements on the order of 0.5 m may be resolved using these methods. Elevation estimate interpretation involves terrace development, degradation, and neotectonics, but this new methodology has significant advantages in studies of neotectonic or geomorphic processes using local terrace elevation measurements.

A 12,000‐year record of vertical deformation across the Yellowstone caldera margin: The shorelines of Yellowstone Lake

The 600 ka Yellowstone caldera exhibits several signs of unrest, the most evident of which is historic ground deformation including both uplift and subsidence. We document deformation in the area of the southeastern caldera across ∼12,000 years using the postglacial shoreline terraces of Yellowstone Lake. Raised shoreline elevations were interpreted from 230 leveling profiles surveyed across flights of terraces, with an accuracy of +/−0.5 m. Of about 11 recognizable terraces, the five most continuous raised shorelines were correlated around the lake basin to reveal deformation patterns. Shoreline ages are based on minimum‐ and maximum‐limiting radiocarbon and obsidian‐hydration dates. Each terrace is interpreted as representing an episode of uplift (∼1 kyr−1) of the caldera interior and subsequent subsidence, with little net volume change. This cyclic behavior may result from magma emplacement and subsequent withdrawal or cooling and crystallization, and/or episodic trapping and release of magmatic fluids (evolved during cooling and crystallization) in a self‐sealing reservoir, as hypothesized by Dzurisin et al. (1990). Early postglacial shoreline deformation reveals substantial intracaldera subsidence, possibly reflecting cooling and loss of trapped hydrothermal fluids. Extension along north‐south trending normal faults and related structures is also apparent in early to middle postglacial deformation both inside and outside of the caldera margin, including downwarping and local faulting of hot, weak intracaldera crust. Net deformation over the past ∼3 kyr has been dominantly up within the caldera interior and slightly down along the caldera rim, relative to the extracaldera region. This uplift is roughly similar to the historic pattern and may largely represent the effects of the most recent inflation episode. Subtraction of the total estimated magnitude of inflation in this episode suggests that the overall trend of postglacial deformation has been subsidence. The cause of this trend is undetermined but is most likely related to the effects of regional extension and long‐term cooling within the Yellowstone caldera.

Geology and petrology of Mahukona Volcano, Hawaii

The submarine Mahukona Volcano, west of the island of Hawaii, is located on the Loa loci line between Kahoolawe and Hualalai Volcanoes. The west rift zone ridge of the volcano extends across a drowned coral reef at about-1150 m and a major slope break at about-1340 m, both of which represent former shoreines. The summit of the volcano apparently reached to about 250 m above sea level (now at-1100 m depth) did was surmounted by a roughly circular caldera. A econd rift zone probably extended toward the east or sutheast, but is completely covered by younger lavas from the adjacent subaerial volcanoes. Samples were vecovered from nine dredges and four submersible lives. Using subsidence rates and the compositions of flows which drape the dated shoreline terraces, we infer that the voluminous phase of tholeiitic shield growth ended about 470 ka, but tholeiitic eruptions continued until at least 435 ka. Basalt, transitional between tholeiitic and alkalic basalt, erupted at the end of tholeiitic volcanism, but no postshield-alkalic stage volcanism occurred. The summit of the volcano apparently subcided below sea level between 435 and 365 ka. The tholeiitic lavas recovered are compositionally diverse.

Scottish freshwater lochs and reservoirs: A physical perspective

Abstract The extensive studies of the Bathymetrical Survey of the Scottish Freshwater Lochs (Murray & Pullar, 1910) provide a background for modern physical limnological research. This paper reviews such investigations in a range of lochs and reservoirs. Resurveying using electronic echo‐sounders and radio position fixing largely confirms the original findings, establishing essentially very low rates of sedimentation. Geophysical sub‐bottom profiling shows sequences of layered deposits upon irregular till surfaces. Sidescan sonar reveals suites of subaqueous landforms such as offshore terraces, depositional fans, scoured channels and blister‐like slides in the organic‐rich silts. The latter may be related to internal seiche movements of the summer thermocline. Shoreline terraces form in coarse marginal deposits in response to wind‐generated, surface wave activity. Sidescan sonar also detects the presence of submerged walls, roads, buildings and former stream channels in artificial impoundments. Fully draw...

Origin and deformation of Holocene shoreline terraces, Yellowstone Lake, Wyoming

Geodetic surveys within the Yellowstone caldera have documented active uplift that is most likely caused by magmatic processes in the upper crust. Along the northeast shore of Yellowstone Lake, maximum relative uplift rates are 10 mm/yr for the period 1923-1975. However, information on deformation prior to historic instrumental records has been lacking. In this study, closely spaced data on elevations of postglacial shoreline terraces around the north end of Yellowstone Lake reveal complex tilting. Though most Holocene deformation is probably magma related, the pattern of shoreline tilting deviates significantly from the historic pattern of roughly symmetric inflation of the caldera. Along the northeast shore, where tilt directions of historic and shoreline deformation are similar, differential uplift of a > 2500-yr-old terrace is roughly 10 m; this gives a maximum uplift rate of 4 mm/yr. These unique Holocene terraces may exist due to episodic deformation because vertical movements affecting the lake outlet directly control lake level.

Direction of absolute movement along the boundary faults of the Basin and Range–Colorado Plateau margin

The direction of absolute movement along the boundary faults of the Basin and Range–Colorado Plateau margin has been determined by comparing present stream profiles with profiles of ancestral streams preserved beneath basalt flows of late Cenozoic age that have been displaced by recurrent movement. Studies of the Grand Wash, Hurricane, and Toroweap faults in southern Utah and northern Arizona indicate that the eastern block or footwall has been the active block and has moved upward, whereas the western block or “downthrown” block has remained essentially stationary. A similar direction of absolute movement on the Wasatch fault in central and northern Utah is apparent from the manner in which Lake Bonneville shoreline terraces have been displaced. These data indicate that recurrent movement along the eastern boundary faults of the Basin and Range rift system is not produced by collapse or subsidence after inflation or uparching of the crust in the rift zone but results from upward-directed stresses. This could be an expression of the direction of mantle movement along the Colorado Plateau-Basin and Range margin.

Upper mantle viscosity derived from the difference in rebound of the Provo and Bonneville Shorelines: Lake Bonneville Basin, Utah

Twenty‐four new field measurements of elevation of Provo level and Bonneville level shoreline terraces provide data for reanalysis of isostatic rebound in the Lake Bonneville basin. Analysis of the differential rebound between the Provo shoreline (maximum rebound of 43 m) and the Bonneville shoreline (maximum rebound of 69 m) requires that the latter be an equilibrium shoreline. Within the possible measurement errors, the Provo shoreline formed after the elastic lithosphere had attained at least 91% equilibration to the removal of the water load between the Bonneville and Provo shorelines; within the errors the Provo may also represent an equilibrium shoreline. From the new data presented in this paper, the best estimate of the upper limit of effective viscosity of the uppermost mantle, assuming a half‐space model and a 2000‐year time interval between the Bonneville and Provo shorelines, is 2 × 1019 N s m−2 (2 × 1020 P). In addition, comparison of shoreline rebound profiles, for both shorelines, with theoretical plate flexure models indicates that the mean flexural rigidity of the Basin and Range lithosphere in this region is 1 × 1023 N m, or slightly less.

A Method to Determine Shingle Supply to the Coast

Relict coastal landforms in Montrose Bay are dominated by shingle particles, which are thought to be derived mainly from inland sources. Standard sediment size and shape parameters and lithology and surface textures of sedimentary particles were used to test this hypothesis. Samples from potential sources of supply to the coast were compared with the properties of relict coastal shingle using bivariate scattergrams. The inland shingle was readily distinguishable from the littoral source types. The relict coastal shingle closely resembled the former. A number of shingle supply phases are distinguished beginning with the Late Devensian deglaciation. Shingle was carried by proglacial streams and later by rivers and deposited in the coastal and offshore zones. It was reworked by marine and river action, particularly during the high sea-level phase of the Flandrian Transgression, and deposited along the coast in the form of shingle bars and river terraces. The use of sediment parameters, along with morphological and stratigraphical evidence, could be applied to other areas to ascertain sediment sources and patterns of supply. THE literature discussing the origin of beach shingle in southern Britain (C. Kidson, 1961, 1966) suggests a supply of material from terrestrial sources with subsequent reworking by marine processes. Research in the Montrose area has attempted to test this hypothesis using standard sedimentary particle parameters. Certain relationships have been shown to exist between the fluid media of transport and deposition and the physical characteristics of the sediment in these media (J. R. L. Allen, I970). Therefore, by measuring the size and shape characteristics of individual particles it should be possible to deduce the sources of shingle deposited along a coast. Furthermore by analysing the morphology, stratigraphy and sedimentary properties of shinglebased landforms a chronology of shingle supply and distribution can be elaborated. It was also hoped to assess the applicability of standard size and shape parameters, derived during studies in the large unigenetic environments of the southern United States, to the differentiation of sedimentary environments in a coastal area of upland Britain. However, this is hindered by the diverse genesis of sedimentary particles in the area since the Late Devensian deglaciation. Here, few particles have been in any one environment sufficiently long for their physical characteristics to be moulded to the equilibrium state which reflects that particular environment. To test both the hypothesis and the method, the sedimentary coast between Montrose and St Cyrus in eastern Scotland was selected (R. S. Crofts, 1971 a, b). A number of well-defined landform groups occur in the area comprising sand beaches, yellow and grey dunes, dune pasture, raised shoreline terraces and fossil cliffs. They are interrupted by the seaward passage of the North and South Esk rivers, leading to the development of a river terrace suite between the dunes and the fossil cliffs along the North Esk course. The raised shoreline and river terraces are the most extensive relict landform groups and they consist largely of shingle (pebbles and cobbles with long axes between 4 and 256 mm). Fossil shingle is also found locally beneath the modern beach and dunes and is one of the dominant constituents of the till and mass-movement debris covering the cliff face. Modern shingle is areally restricted, occurring on the bed of the

NOTES SUR LE PERIGLACIAIRE DU SPITZBERG

RéSUMé From the first, inquiries into periglacial morphology in Spitsbergen (beginning in 1910) have tended to direct the world's periglacial research to the study of patterned ground. In Spitsbergen, periglacial forms are related to both climatic and locational factors. The gelival cycle, the fluvioperiglacial phenomena, floating ice conditions, the semi-arid regime, and a wide range of seasonal contrasts are the main climatic features. The numerous shoreline terraces constitute a terrain favourable to the development of both certain sediments and surface forms. The author's classification of periglacial phenomena comprises the following groups: (1) perigelisol and mollisol; (2) patterned ground; (3) gelifraction and slides; (4) gelifluction; (5) floating ice conditions; (6) glacial tectonics; (7) others. The rhythm of evolution of periglacial phenomena in Spitsbergen has not been the same in all parts; therefore the observed forms usually carry traces of various climatic fluctuations; slopes and patterned ground in particular show the effect of these “read-vances” of glacial climatic conditions. The paper ends with an appended glossary of more than thirty technical terms.

Observations on the Drainage of a Glacier-Dammed Lake in Norway

AbstractThe behaviour of a Norwegian glacier-dammed lake, before, during and after drainage in 1957 is described. The evidence of former shoreline terraces is interpreted and possible drainage mechanisms are discussed.

Observations on the Drainage of a Glacier-Dammed Lake in Norway

Abstract The behaviour of a Norwegian glacier-dammed lake, before, during and after drainage in 1957 is described. The evidence of former shoreline terraces is interpreted and possible drainage mechanisms are discussed.