Marine geophysicist. Working on a number of topics from marine landslides, to tectonics and remote sensing. ICDP project manager for the Dead Sea Deep borehole
The Halutza, Agur and Shunra sand dunes are the continuation of the great northern Sinai dunes. P... more The Halutza, Agur and Shunra sand dunes are the continuation of the great northern Sinai dunes. Playa sediments from the late Quaternary are found on upper parts of river channels in the area of the dunes of the Northwest Negev and represent disorder in the drainage ...
The Israeli coastline is generally characterized by a broad and shallow continental shelf. Akhziv... more The Israeli coastline is generally characterized by a broad and shallow continental shelf. Akhziv submarine canyon (ASC), in its northern reach, creates a locally unique marine ecosystem. The present study is the first to investigate the benthic macro-fauna of ASC, in order to assess its importance as a potential productivity ‘hotspot’ within its ultra-oligotrophic surroundings. Seven research cruises were conducted during 2010-2013, along ASC’s two channels and at iso-bathic control sites on the adjacent slope (AS), encompassing 8 sampling stations, at depths of 40-450 m. Bottom samples were collected by a Van Veen Grab, gravity corer and a GOMEX box corer. The infauna (≥500 µm) were counted and identified to the lowest possible taxonomic level. Sediments were analysed for grain size & composition and total organic carbon concentration. Mean benthic macro-faunal abundance (individuals/500ml ± SD) was higher inside the canyon (13.0±19.4) compared to the AS (2.9±3.3) (p=0.004), as wa...
The autumn 2008 cruise of Charney School of Marine Sciences (CSMS) was focused on high resolution... more The autumn 2008 cruise of Charney School of Marine Sciences (CSMS) was focused on high resolution geological and geophysical investigation of the outer continental shelf (50 to 85 m seafloor depth) offshore Haifa Bay, Israel. The cruise corroborated collection of an oceanographic transect, acquisition of a grid of 2 km long high resolution (~1-2.5 kHz) single channel seismic reflection profiles
Geology usually deals with rocks formed long ago, which are static and stable over the span of hu... more Geology usually deals with rocks formed long ago, which are static and stable over the span of human lifetime. This study aims to analyze anthropogenic influence on the formation of geological features in the southeastern Mediterranean. Tel Dor, along Israel’s northern coast, was chosen due to the continuous presence of humans in the area for over 4000 years and the protective environment of its natural bays that preserve geomorphological changes. This allows for the examination of whether and how humans affect their (geological) environment. Three rocky platforms were chosen in the shallow waters of the South Bay adjacent to the Tel, and four cores were extracted. Results show the extent of the direct and indirect anthropological influences on the landscape. The presence of building stones consisting of dolomite, which is not found along the Carmel coast, is an example of direct influence (importation). The evolution of a biological and non-biological reef upon the sturdy base of t...
Following the Last Glacial Maximum (LGM) lowstand, global sea-level rose by ~120m flooding previo... more Following the Last Glacial Maximum (LGM) lowstand, global sea-level rose by ~120m flooding previously exposed continental shelves worldwide with water and sediments. In these drowned environments sediment accumulation patterns are dictated by a superposition of vertical tectonic motion, sea-level change and sediment supply rates, which are hard to distinguish from one another. This study focuses on a unique region where
Observed gravity data after latitude, elevation (free air), Bouguer and terrain corrections deter... more Observed gravity data after latitude, elevation (free air), Bouguer and terrain corrections determine “the sum of all effects from the grass roots down” (Nettleton, 1971). In order to eliminate gravity effects corresponding to unwanted disturbances in the subsurface, various approaches can be used. One such approach that has proven the test of time is gravity interpretation by stripping (e.g., Woollard, 1938; Bible, 1961; Hammer, 1963). The removal of an effect of a known density contrast (i.e., constrained by independent geophysical and geological data) allows determination of gravity corresponding to other targets of interest. It is well known that the advantage of the gravity-stripping procedure is that it is more accurate than any mathematical (convolution) method for separation of the gravity field (including filtering procedures), as the latter contain not only information on the amplification of available gravity components, but also false anomalies. Moreover, all transformed...
ABSTRACT The Eshet Ridge is located in the central Arava near Wadi Paran. Geological data were co... more ABSTRACT The Eshet Ridge is located in the central Arava near Wadi Paran. Geological data were collected using ground magnetic surveys and petrophysical measurements (magnetic susceptibility and density). The goal was to reveal the structure and nature of a concealed magmatic body under the ridge. Integrated gravity and magnetic interpretation together with seismic reflection data (including 2¾ modeling) indicated the presence of a deep-seated basic magmatic intrusion. Occurrence of Fe-mineralized rocks along the ridge supports subsurface data. The magmatic body was intruded in the hard Turonian rocks of the Eshet Ridge. Basic magmatic exposures dating from the Early Miocene were evident along Wadi Ashosh (in the eastern Negev) and its margins 18 km. to the north of the ridge. A new outcrop of basic magmatic intrusion was found southwest of the Tzukim settlement. Magnetic measurements indicated a similarity between their magnetic pattern and the Ashosh basic magmatics, which were dated to 20.4±0.7 Ma. Volcanoclastic tuff pebbles (magnetic susceptibility of around 2–7 ∗ 10-3 SI) surrounded by conglomerate were discovered at two sites in Wadi Demma and Wadi Menuha (streams that drain near the Eshet Ridge and 2 km. south of it, respectively). The conglomerates contained mostly limestone, chalk and chert fragments; not more than 5% of which were volcanic pebbles. Two pebbles were dated to 24.4±0.7and 21.5±0.5 Ma. The magmatic outcrops in Wadi Ashosh, the magmatic dyke near Tzukim and the volcanic purple and black pebbles near Wadi Menuha were all dated to the very Late Oligocene - Early Miocene. The magmatic body identified in this study under the Eshet Ridge was termed the Eshet Intrusion and is connected to, and even the source of, all these phenomena.
ABSTRACT The Red Sea is part of a long system of rifts, which formed as a result of African–Arabi... more ABSTRACT The Red Sea is part of a long system of rifts, which formed as a result of African–Arabian continental breakup during the Oligocene–Miocene. Two phases of volcanism are generally accepted, the first occurring 31 mya and the second ∼25 mya. Sometime between 20 and 14 Ma motion along the Dead Sea fault developed and new plate geometry arose to reflect the collision of Arabia with Eurasia. As a result, extension along the northern Red Sea switched from rift-normal (N60°E) to highly oblique and parallel to the newly formed fault. Sea-floor spreading commenced in the southern Red Sea at about 5 Ma leading to a change in the way extension is accommodated along its length. In general the Red Sea is divided into three segments with distinct morphologies and geophysical characteristics: southern (between 15°N and 20°N) – active seafloor spreading, central transition zone (20–23.3°N) with discontinuous axial trough and isolated cells of seafloor spreading, northern dominated by an axial depression is currently in the late stages of continental rifting. Magnetic and gravity data support the differences between the southern and northern sections, while new tomographic studies indicate that the central section behaves as a separate entity that does not act as a transfer zone that gradually transmits processes from south to north. Rifting in the southern Red Sea is under the influence of the Afar plume, while in the north, new evidence points to a strong connection with the Dead Sea fault (fault-parallel and perpendicular features indicating motion parallel to the fault). Motion along the fault may be the stronger force acting on the northern Red Sea and hence, it will behave differently than the southern section. The northern section may act as an area, which transfers motion from seafloor spreading (central-southern Red Sea) to strike-slip (Dead Sea fault).
ABSTRACT This study explores, for the first time, the response of the Mediterranean seafloor to d... more ABSTRACT This study explores, for the first time, the response of the Mediterranean seafloor to desiccation and its affect on climate during the Messinian lowstand. New high-resolution 3-D pre-stack depth migrated seismic reflection data show evidence for gas outflow stemming from pre-Messinian sources. Our results indicate that giant pockmarks formed during this lowstand. Emission continued throughout the Messinian and persisted after it ended as evident by pockmark arrays on the then-seafloor. High reflectivity between the top-Messinian and overlying Pliocene sediments indicates significant gas accumulation immediately below the latter. Attribute analysis show minor chaotic paths through the Plio-Pleistocene, which do not reach the present-day seafloor. Our data indicate that as long as sea level was low there was massive gas escape to the shallow sea and atmosphere. We suggest that this probably resulted in the mid-Messinian climatic shift. Major emissions identified here indicate an indirect cause to negative climatic feedback during this period.
ABSTRACT An active gas migration system across the eastern Mediterranean continental shelf, offsh... more ABSTRACT An active gas migration system across the eastern Mediterranean continental shelf, offshore northern Israel, is described for the first time. Seven vintages of industrial multi-channel seismic reflection and high-resolution single-channel data are integrated with data from a deep borehole, bathymetry and backscatter maps. Combined interpretation, aided by seismic attribute analysis, exhibits a variety of seismic gas signatures across the subsurface and seabed: acoustic blanking, bright spots, phase reversals, gas chimneys, reflector smearing, pockmarks and presumed gas release into the water column. Sub-seafloor gas stems from three main sources: (1) Mid-Pleistocene and (2) Last Glacial Maximum unconformities and (3) a series of incised channels in-between which are also related to glacial maxima. Close to the seafloor, gas accumulates across an area of 72 km2 at depths ranging from 37-112 m below sea-level, while ~720 pockmarks pierce the seafloor mainly at the gas front periphery. Active emission from one seep at the seafloor was recorded repeatedly over three years. We hypothesize that the well developed active gas system shown here for the first time is not unique to the continental shelf off northern Israel. Conversely, it represents the usually underestimated marine methane contribution from mid-latitude continental shelves into the marine environment and maybe into the atmosphere. This study suggests that global warming and sea level rise induces a negative, restraining feedback for gas emission across mid-latitude continental margins and thus being inverse to high latitudes, where this feedback is most likely positive due to the stronger impact of bottom water warming.
Geology usually deals with rocks formed long ago, which are static and stable over the span of hu... more Geology usually deals with rocks formed long ago, which are static and stable over the span of human lifetime. This study aims to analyze anthropogenic influence on the formation of geological features in the southeastern Mediterranean. Tel Dor, along Israel’s northern coast, was chosen due to the continuous presence of humans in the area for over 4000 years and the protective environment of its natural bays that preserve geomorphological changes. This allows for the examination of whether and how humans affect their (geological) environment. Three rocky platforms were chosen in the shallow waters of the South Bay adjacent to the Tel, and four cores were extracted. Results show the extent of the direct and indirect anthropological influences on the landscape. The presence of building stones consisting of dolomite, which is not found along the Carmel coast, is an example of direct influence (importation). The evolution of a biological and non-biological reef upon the sturdy base of the port constructions is an indirect influence. The formation of a non-biological reef upon an archaeological feature is a unique process. It would not have consolidated without the presence of anthropogenic activity. This study shows how human interference in the coastal area can trigger a chain reaction of geological processes lasting more than 2000 years.
The Halutza, Agur and Shunra sand dunes are the continuation of the great northern Sinai dunes. P... more The Halutza, Agur and Shunra sand dunes are the continuation of the great northern Sinai dunes. Playa sediments from the late Quaternary are found on upper parts of river channels in the area of the dunes of the Northwest Negev and represent disorder in the drainage ...
The Israeli coastline is generally characterized by a broad and shallow continental shelf. Akhziv... more The Israeli coastline is generally characterized by a broad and shallow continental shelf. Akhziv submarine canyon (ASC), in its northern reach, creates a locally unique marine ecosystem. The present study is the first to investigate the benthic macro-fauna of ASC, in order to assess its importance as a potential productivity ‘hotspot’ within its ultra-oligotrophic surroundings. Seven research cruises were conducted during 2010-2013, along ASC’s two channels and at iso-bathic control sites on the adjacent slope (AS), encompassing 8 sampling stations, at depths of 40-450 m. Bottom samples were collected by a Van Veen Grab, gravity corer and a GOMEX box corer. The infauna (≥500 µm) were counted and identified to the lowest possible taxonomic level. Sediments were analysed for grain size & composition and total organic carbon concentration. Mean benthic macro-faunal abundance (individuals/500ml ± SD) was higher inside the canyon (13.0±19.4) compared to the AS (2.9±3.3) (p=0.004), as wa...
The autumn 2008 cruise of Charney School of Marine Sciences (CSMS) was focused on high resolution... more The autumn 2008 cruise of Charney School of Marine Sciences (CSMS) was focused on high resolution geological and geophysical investigation of the outer continental shelf (50 to 85 m seafloor depth) offshore Haifa Bay, Israel. The cruise corroborated collection of an oceanographic transect, acquisition of a grid of 2 km long high resolution (~1-2.5 kHz) single channel seismic reflection profiles
Geology usually deals with rocks formed long ago, which are static and stable over the span of hu... more Geology usually deals with rocks formed long ago, which are static and stable over the span of human lifetime. This study aims to analyze anthropogenic influence on the formation of geological features in the southeastern Mediterranean. Tel Dor, along Israel’s northern coast, was chosen due to the continuous presence of humans in the area for over 4000 years and the protective environment of its natural bays that preserve geomorphological changes. This allows for the examination of whether and how humans affect their (geological) environment. Three rocky platforms were chosen in the shallow waters of the South Bay adjacent to the Tel, and four cores were extracted. Results show the extent of the direct and indirect anthropological influences on the landscape. The presence of building stones consisting of dolomite, which is not found along the Carmel coast, is an example of direct influence (importation). The evolution of a biological and non-biological reef upon the sturdy base of t...
Following the Last Glacial Maximum (LGM) lowstand, global sea-level rose by ~120m flooding previo... more Following the Last Glacial Maximum (LGM) lowstand, global sea-level rose by ~120m flooding previously exposed continental shelves worldwide with water and sediments. In these drowned environments sediment accumulation patterns are dictated by a superposition of vertical tectonic motion, sea-level change and sediment supply rates, which are hard to distinguish from one another. This study focuses on a unique region where
Observed gravity data after latitude, elevation (free air), Bouguer and terrain corrections deter... more Observed gravity data after latitude, elevation (free air), Bouguer and terrain corrections determine “the sum of all effects from the grass roots down” (Nettleton, 1971). In order to eliminate gravity effects corresponding to unwanted disturbances in the subsurface, various approaches can be used. One such approach that has proven the test of time is gravity interpretation by stripping (e.g., Woollard, 1938; Bible, 1961; Hammer, 1963). The removal of an effect of a known density contrast (i.e., constrained by independent geophysical and geological data) allows determination of gravity corresponding to other targets of interest. It is well known that the advantage of the gravity-stripping procedure is that it is more accurate than any mathematical (convolution) method for separation of the gravity field (including filtering procedures), as the latter contain not only information on the amplification of available gravity components, but also false anomalies. Moreover, all transformed...
ABSTRACT The Eshet Ridge is located in the central Arava near Wadi Paran. Geological data were co... more ABSTRACT The Eshet Ridge is located in the central Arava near Wadi Paran. Geological data were collected using ground magnetic surveys and petrophysical measurements (magnetic susceptibility and density). The goal was to reveal the structure and nature of a concealed magmatic body under the ridge. Integrated gravity and magnetic interpretation together with seismic reflection data (including 2¾ modeling) indicated the presence of a deep-seated basic magmatic intrusion. Occurrence of Fe-mineralized rocks along the ridge supports subsurface data. The magmatic body was intruded in the hard Turonian rocks of the Eshet Ridge. Basic magmatic exposures dating from the Early Miocene were evident along Wadi Ashosh (in the eastern Negev) and its margins 18 km. to the north of the ridge. A new outcrop of basic magmatic intrusion was found southwest of the Tzukim settlement. Magnetic measurements indicated a similarity between their magnetic pattern and the Ashosh basic magmatics, which were dated to 20.4±0.7 Ma. Volcanoclastic tuff pebbles (magnetic susceptibility of around 2–7 ∗ 10-3 SI) surrounded by conglomerate were discovered at two sites in Wadi Demma and Wadi Menuha (streams that drain near the Eshet Ridge and 2 km. south of it, respectively). The conglomerates contained mostly limestone, chalk and chert fragments; not more than 5% of which were volcanic pebbles. Two pebbles were dated to 24.4±0.7and 21.5±0.5 Ma. The magmatic outcrops in Wadi Ashosh, the magmatic dyke near Tzukim and the volcanic purple and black pebbles near Wadi Menuha were all dated to the very Late Oligocene - Early Miocene. The magmatic body identified in this study under the Eshet Ridge was termed the Eshet Intrusion and is connected to, and even the source of, all these phenomena.
ABSTRACT The Red Sea is part of a long system of rifts, which formed as a result of African–Arabi... more ABSTRACT The Red Sea is part of a long system of rifts, which formed as a result of African–Arabian continental breakup during the Oligocene–Miocene. Two phases of volcanism are generally accepted, the first occurring 31 mya and the second ∼25 mya. Sometime between 20 and 14 Ma motion along the Dead Sea fault developed and new plate geometry arose to reflect the collision of Arabia with Eurasia. As a result, extension along the northern Red Sea switched from rift-normal (N60°E) to highly oblique and parallel to the newly formed fault. Sea-floor spreading commenced in the southern Red Sea at about 5 Ma leading to a change in the way extension is accommodated along its length. In general the Red Sea is divided into three segments with distinct morphologies and geophysical characteristics: southern (between 15°N and 20°N) – active seafloor spreading, central transition zone (20–23.3°N) with discontinuous axial trough and isolated cells of seafloor spreading, northern dominated by an axial depression is currently in the late stages of continental rifting. Magnetic and gravity data support the differences between the southern and northern sections, while new tomographic studies indicate that the central section behaves as a separate entity that does not act as a transfer zone that gradually transmits processes from south to north. Rifting in the southern Red Sea is under the influence of the Afar plume, while in the north, new evidence points to a strong connection with the Dead Sea fault (fault-parallel and perpendicular features indicating motion parallel to the fault). Motion along the fault may be the stronger force acting on the northern Red Sea and hence, it will behave differently than the southern section. The northern section may act as an area, which transfers motion from seafloor spreading (central-southern Red Sea) to strike-slip (Dead Sea fault).
ABSTRACT This study explores, for the first time, the response of the Mediterranean seafloor to d... more ABSTRACT This study explores, for the first time, the response of the Mediterranean seafloor to desiccation and its affect on climate during the Messinian lowstand. New high-resolution 3-D pre-stack depth migrated seismic reflection data show evidence for gas outflow stemming from pre-Messinian sources. Our results indicate that giant pockmarks formed during this lowstand. Emission continued throughout the Messinian and persisted after it ended as evident by pockmark arrays on the then-seafloor. High reflectivity between the top-Messinian and overlying Pliocene sediments indicates significant gas accumulation immediately below the latter. Attribute analysis show minor chaotic paths through the Plio-Pleistocene, which do not reach the present-day seafloor. Our data indicate that as long as sea level was low there was massive gas escape to the shallow sea and atmosphere. We suggest that this probably resulted in the mid-Messinian climatic shift. Major emissions identified here indicate an indirect cause to negative climatic feedback during this period.
ABSTRACT An active gas migration system across the eastern Mediterranean continental shelf, offsh... more ABSTRACT An active gas migration system across the eastern Mediterranean continental shelf, offshore northern Israel, is described for the first time. Seven vintages of industrial multi-channel seismic reflection and high-resolution single-channel data are integrated with data from a deep borehole, bathymetry and backscatter maps. Combined interpretation, aided by seismic attribute analysis, exhibits a variety of seismic gas signatures across the subsurface and seabed: acoustic blanking, bright spots, phase reversals, gas chimneys, reflector smearing, pockmarks and presumed gas release into the water column. Sub-seafloor gas stems from three main sources: (1) Mid-Pleistocene and (2) Last Glacial Maximum unconformities and (3) a series of incised channels in-between which are also related to glacial maxima. Close to the seafloor, gas accumulates across an area of 72 km2 at depths ranging from 37-112 m below sea-level, while ~720 pockmarks pierce the seafloor mainly at the gas front periphery. Active emission from one seep at the seafloor was recorded repeatedly over three years. We hypothesize that the well developed active gas system shown here for the first time is not unique to the continental shelf off northern Israel. Conversely, it represents the usually underestimated marine methane contribution from mid-latitude continental shelves into the marine environment and maybe into the atmosphere. This study suggests that global warming and sea level rise induces a negative, restraining feedback for gas emission across mid-latitude continental margins and thus being inverse to high latitudes, where this feedback is most likely positive due to the stronger impact of bottom water warming.
Geology usually deals with rocks formed long ago, which are static and stable over the span of hu... more Geology usually deals with rocks formed long ago, which are static and stable over the span of human lifetime. This study aims to analyze anthropogenic influence on the formation of geological features in the southeastern Mediterranean. Tel Dor, along Israel’s northern coast, was chosen due to the continuous presence of humans in the area for over 4000 years and the protective environment of its natural bays that preserve geomorphological changes. This allows for the examination of whether and how humans affect their (geological) environment. Three rocky platforms were chosen in the shallow waters of the South Bay adjacent to the Tel, and four cores were extracted. Results show the extent of the direct and indirect anthropological influences on the landscape. The presence of building stones consisting of dolomite, which is not found along the Carmel coast, is an example of direct influence (importation). The evolution of a biological and non-biological reef upon the sturdy base of the port constructions is an indirect influence. The formation of a non-biological reef upon an archaeological feature is a unique process. It would not have consolidated without the presence of anthropogenic activity. This study shows how human interference in the coastal area can trigger a chain reaction of geological processes lasting more than 2000 years.
An on‐land frequency domain electromagnetic geophysical survey was conducted across a tombolo del... more An on‐land frequency domain electromagnetic geophysical survey was conducted across a tombolo delimiting the southern bay of Tel Dor (northern Israel) to the south. It was accompanied by a marine archaeological survey adjacent to its northern edge. Results indicate a deep channel connecting the bay and the Tantura Lagoon to the south. At its northern exit, an NW–SE trending square anomaly is visible in the geophysical data, buried underneath centuries of sand accumulation. It is parallel and similar in shape and scale to a Hellenistic feature observed in satellite data and excavated during the underwater archaeological survey. It seems that during the beginning/Middle Bronze Age, a natural or manmade channel was utilized as an entrance to the bay. As sea levels rose and sand began to accumulate, the channel was periodically filled in and would have needed to have been cleared. Eventually, it became too expensive or inconvenient to maintain, probably during the Byzantine period. The southern anchorage was abandoned for more favorable conditions to the north of the Tel. The sequence of events shows how ancient builders first utilized a natural channel, maintained it as sea levels rose, and abandoned it when it became too problematic to maintain.
Along the Levantine coast, ancient anchorages facilitated urban center establishment by enabling ... more Along the Levantine coast, ancient anchorages facilitated urban center establishment by enabling travel between sites and civilizations, leading to expanding trade networks. Various scholars have hypothesized that growing maritime economic prosperity during the Bronze and Iron Ages was permitted along the Israeli coast in Yaffo, Dor, Tel Naami, Tel Akko, and Tel Achziv due to natural processes in the marine-terrestrial interface and subsequent development of lagoonal systems. Once formed, these natural, protected aquatic systems were postulated to have been utilized by the coastal inhabitants as inland harbors constructed adjacent to the settlement. Here the complex long-term relationships between sea-level rise, sedimentation variation, and resulting coastal morphogenesis are examined in the area of Tel Dor in order to assess if an inland anchorage existed adjacent to the Middle Bronze – Iron age site. This investigation relies on a high-resolution spatial and temporal paleoenvironmental record combining dated terrestrial and shallow marine sediment cores with sedimentological and faunal analyses as well as seismic profiles collected from the shallow marine South Bay of Dor. The current stratigraphic framework indicates that the coast of Dor has undergone morphological changes during the Holocene. These consist of a brackish wetland environment (ca. 9 ₋ 7 ka) that changed to a high energy beach (ca. 7 ₋ 4 ka) and finally became a backshore influenced by anthropogenic activity of the coastal inhabitants (4 ka ₋ present). The Holocene stratigraphy, the surface elevation of each lithological unit, and association with sea level variation over the last 9 ka rule out the existence of a lagoon. As a result, it is unlikely that the area facilitated an inland anchorage, making previous hypotheses on this matter unplausible. Our holistic approach at Dor provides a unique opportunity for studying ancient coastal processes, which are essential for properly understanding the interplay between the varying environment and coastal settlers.
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Papers by Michael Lazar
Lagoon to the south. At its northern exit, an NW–SE trending square anomaly is visible in the geophysical data, buried underneath centuries of sand accumulation. It is parallel and similar in shape and scale to a Hellenistic feature observed in satellite data and excavated during the underwater archaeological survey. It seems that during the beginning/Middle Bronze Age, a natural or manmade channel was utilized as an entrance to the bay. As sea levels rose and sand began to accumulate, the channel was periodically filled in and would have needed to have been cleared. Eventually, it became too expensive or inconvenient to maintain, probably during the Byzantine period. The southern anchorage was abandoned for more favorable conditions to the north of the Tel. The sequence of events shows how ancient builders first utilized a natural channel, maintained it as sea levels rose, and abandoned it when it became too problematic to maintain.