Submarine features formed in the coastal zone as a result of the Hans Glacier retreat and the impact of oceanographic conditions (Hornsund, Isbjørnhamna, Hansbukta)
Authors:
Joanna Ćwiąkała ([email protected]), Mateusz Moskalik ([email protected])
Institute of Geophysics, Polish Academy of Sciences - Centre for Polar Studies KNOW (Leading National Research Centre)
Introduction: Study area: Description of the maps on the poster
The studies of a seafloor in the fjords of Spitsbergen are very The Isbjørnhamna is located in the outer part of the Hornsund fjord. Maps show the bathymetry and the relief of seabed in Isbjørnhamna important to know the past of the tidewater glaciers and the glacial It is bordered by Hansbukta from the north. The tidewater Hans and Hansbukta. Figure one shows the bathymetry map of study submarine morphology. The modern geophysical equipment such as Glacier is located in the north-east part of Hansbukta. This bay is areas. We can see that these bays are not deep. The deepest part of multibeam echousounder can be used to make a precise growing all time, as a result of the Hans Glacier retreat. bays is near the ice cliff (about 90-100 m). The shallowest parts of bathymetry map of the seafloor in the fjords, which can reveal all The total area of the study covers about 6,5 km². The location of bays are near the shores and on the terminal moraine. landforms on the seabed. This study focuses mainly on identification those bays causes that the Greenland Sea has a big impact on its The second figure shows the geomorphology map of the seabed of and description of the glacial submarine morphology of oceanographic conditions. The oceanographic conditions and Hans Isbjørnhamna and Hansbukta. We can distinguish 10 different Isbjørnhamna and Hansbukta. The important aim of this study is to glacier retreat cause changes in the bottom of the bays. The relief of features on the seabed. These forms are mainly of glacial and marine attempt to explain genesis of these forms, too. the bottom of Isbjørnhamna and Hansbukta are very diverse. genesis.
Legend
Flat areas
„Leaf”
Pits (chain, circular)
Plough marks
Pockmarks
Ridges of recessional moraines
Ripple marks
Submarine mass movements
Terminal moraine with ridge
Underwater rocks and skerries
Shoreline Source: Authors' own elaboration based on: -depth data from The Norwegian Hydrographic Service with permit number 13/G722, - Norwegian Polar Institute. (2014). Kartdata Svalbard 1:100 000 (S100 Kartdata). Tromsø, Norway: Norwegian Polar Institute, -https://data.npolar.no/dataset/645336c7-adfe-4d5a-978d- Fig . The bathymetry map of Isbjørnhamna and Hansbukta Fig 2. The geomorphological map of Isbjørnhamna and Hansbukta 9426fe788ee3.
Features on the seafloor of Isbjørnhamna and Hansbukta: Recessional moraines - Moraine hills form after the winter advance of glacier. They are located near the ice cliff. They form a ridges, hummock or hills. They are made by till, rocks, sand and gravel. These ridges allow to locate the position of the glacier Flat areas - They are forms of accumulations. Fine-grained sediments are transported by shallow-water currents. These from year to year. When the glacier advances further than the annual moraine, it causes destruction of this moraine. sediments fall very slowly in water. These features can cover older forms. The eight of transverse recessional moraines are located in front of ice cliff in Hansbukta. These ridges are located subparallel The four flat areas in Isbjørnhamna and Hansbukta are located between the terminal moraine and ice cliff. They are in the to one another on the section to 1 km of length. The longest ridge of moraine is about 1,1 km. The width of these moraines central part of the bays. They are divided by the rock sills and the ridges of recessional moraines. The depths range from 21 does not exceed 100 m. They are lower in the central parts and higher on the edges. Some of them are completely interrupted to 58 m. The smallest flat area is about 0.035 km2 and the biggest flat area is about 0.43 km2. The biggest flat area consists in the central part of the bay. The flat areas are located between these moraines. of two parts, which are partly divided by the transverse rock sill. Pockmarks are located on the south part of this flat area. Samples articles about forms: Other form, like submarine mass movements end on these flat areas. Ottesen D., Dowdeswell J.A., 2006, Assemblages of submarine landforms produced by tidewater glaciers in Svalbard, Journal of Geophysical Research 111. Ottesen D., Dowdeswel J.A., Benn D.I., Kristensen L., Christiansen H.H., Christensen O., Hansen L., Lebesbye E., Forwick M., Vorren T.O., 2008, Submarine „Leaf”- This concave form is located in fined-grained sediment deposition, on the flat area. The shape of feature looks landforms characteristic of glacier surges in two Spitsbergen fjords, Quaternary Science Review 27, 1583-1599. similar to leaf of linden. It is kind of flat area, which is located on another flat area. The surface of “leaf” is 0.015 km². We do Dowdeswell J.A., Vasquez ., 2013, Submarine landforms in the fjords of southern Chile: implications for glacimarine processes and sedimentation in a mild not know what the genesis of this feature is. glacier-influenced environment, , Quaternary Science Review 64, 1-19. Samples articles about forms: Ottesen D., Dowdeswell J.A., 2009, An inter-ice-stream glaciated margin: Submarine landforms and a geomorphic model based on marine-geophysical data Ripple marks- They are wavy wrinkles made of grainy material. They are formed by the movement of non-cohesive grainy from Svalbard, Geological Society of America Bulletin 121, 1647-1665. Dowdeswell J.A., Vasquez ., 2013, Submarine landforms in the fjords of southern Chile: implications for glacimarine processes and sedimentation in a mild material. Movement of the material is caused by motion of water (waves, currents and tides). Shapes of the ripple marks glacier-influenced environment, , Quaternary Science Review 64, 1-19. indicate a direction of water. In Isbjørnhamna and Hansbukta, ripple marks are located on the shallower areas (to 25 m of depth). They are located mainly Pits- These forms are the holes located on the shallower parts of the bays and seas. They have similar genesis to the in the eastern part of the bays, along the shore and on the terminal moraine. The number of fields of ripple marks is more than plough marks (iceberg genesis). The iceberg keels plough the seabed and form chain pits or circular pits. Both kinds of these 125. The biggest fields of ripple marks are on the terminal moraine. The biggest field of ripple marks is located on the central features are located on the shallow water, near shores. The circular pits form when the floating rapidly settles on the seabed part of terminal moraine and its size is 0.052 km2. At the shore, fields of ripple marks are small, and they are situated near under the influence of the tides or wave. The inflow lifts and relocates the icebergs. During the outflow the iceberg settles rocks. again. In this situation the prints of icebergs are the circular pits. Chain pits are formed during the displacement of an iceberg, it fluctuates to the seabed at all times. The furrow is ploughed in the seabed and bounces off the bottom. Submarine mass movements- They are caused by the force gravity. The submarine mass movements are differentiated The both types of pits are located near the shores, on the shallower areas in Isbjørnhamna and Hansbukta. The total number from those on the land. The most common reasons of landslides and other submarine mass movements are: the unstable of them is about 240. The most of them are near the east shore of the bays. Near the west part of the shores of bays, pits geological layers, the overpressure (the result of the fast accumulation of sedimentary processes), storm waves, earthquakes, are clustered around the Baranowskiodden. In turn, in the east part of bays, they are distributed along the entire east coast. gas hydrate, the activity of the glaciers and volcanos, groundwater seepage and high poor water pressure, and oversteeping. Samples articles about forms: These movements may be fast and rapid or slow and hard to the observation. The violent submarine mass movements Davidson S.H., Simms A., 1997, Enviromental Studies Research Funds: Characterisation of iceberg pits on the Grand Banks of Newfoundland, Report 133, include e.g. landslide and debris flows. The slow mass movement is e.g. downhill creep. p.167. Hill J.C., Gayes P.T., Driscoll N.W., Johnstone E.A., Sedberry G.R., 2008, Iceberg scours along the southern U.S. Atlantic margin, Geology 36, 447-450. The nine of submarine mass movements are located near moraine ridges in Isbjørnhamna and Hansbukta. The mass wasting are less than 100 years old. They started to form after the Hans Glacier retreat and the creation of flat areas in the inner parts Plough marks –these landforms are the furrows in the seafloor and they are formed by iceberg keels. Icebergs are of the bays. The biggest mass movements are on the south slope of the terminal moraine. The next mass movements are on transported by currents into shallow areas. Plough marks form during these movements. They plough the sediment the slopes of the rock sills and the other moraines. The biggest submarine mass movement is 0.48 km2 and is located exactly depositions. Icebergs scours can be long or short, narrow or wide and deep or shallow. The shapes depends on size of on the outer part of the terminal moraine. iceberg, type of seafloor and oceanographic conditions. Samples articles about forms: Bozzano F., Mazzanti P., Anzidei M., Esposito C., Flrois M., Bianchi Fasani G., Esposito A., 2009, Slope dynamics of Lake Albano (Rome, The icebergs scours are located on the periphery of bays. Plough marks dominate in the eastern part of the bays. They Italy): insights from high resolution bathymetry, Earth Surface processes and landforms 34, 1469-1486. occupy a shallower areas (to about 20 m of depth). They are located along the shores, from terminal moraine (from LIA) to ridges of annual moraines near the cliff of the glacier. The number of plough marks is more than 150. The longest plough Terminal moraine- Form sets a maximum limit of the position glacier. This moraine is parallel to the glacier front. This feature mark is 155 m. It is located in the north-eastern part of Hansbukta, on 12 m of depth. forms during glacier stagnation. Terminal moraines are formed by the accumulation of material, mainly till, rocks, gravel and Samples articles about forms: Ottesen D., Dowdeswell J.A., 2013, Buried iceberg ploughmarks in the early Quaternary sediments of the central North Sea: a two-milion year record of sand. Other action which causes form moraines is squeezing ground formations by ice cliff. The shape of terminal moraine is glacial influence fro 3D seismic data, Marine Geology 344, 1-9. similar to the ridges, hummock or hill. Dowdeswell J.A., Vasquez ., 2013, Submarine landforms in the fjords of southern Chile: implications for glacimarine processes and sedimentation in a mild Terminal moraine in Isbjørnhamna was formed the end of Little Ice Age. This moraine has it extension on both shores (west glacier-influenced environment, , Quaternary Science Review 64, 1-19. and east) of Isbjørnhamna. The bottom of the bay is shallower from the north side of the terminal moraine. The border of the bay is marked by the south side of terminal moraine in the east part of this area. The west side of area, behind the moraine is Pockmarks-They are concave formations formed on the surface of sediment deposits. Pockmarks are similar to the geological craters (Forwick et al. 2009). They may have a few hundred meters in diameter. Pockmarks are the result of submarine freshwater outflows and shallow and is a part of the Isbjørnhamna. The total area of this moraine under a water is 1.54 km2. This feature is border for thermogenic or biogenic filtration of gases. Furthermore, these formations may have formed during the natural catastrophes (Harrington most forms with glacier genesis. The length of this moraine is about 3.3 km under water. 1985, Rogers 2006, Forwick et al. 2009). Due to the pockmarks morphology we can distinguish: circular (often with raised rims), elliptical, Samples articles about forms: asymmetric and composite pockmarks (Judd, Hovland 2007, Forwick et a. 2009). They may be formed in lakes, fjords, estuaries, slopes, Ottesen D., Dowdeswell J.A., 2006, Assemblages of submarine landforms produced by tidewater glaciers in Svalbard, Journal of Geophysical Research 111. Ottesen D., Dowdeswel J.A., Benn D.I., Kristensen L., Christiansen H.H., Christensen O., Hansen L., Lebesbye E., Forwick M., Vorren T.O., 2008, Submarine continental shelves and shallow bays (Pickrill 1993, Rogers 2006, Gay et al. 2007, Forwick et al. 2009). landforms characteristic of glacier surges in two Spitsbergen fjords, Quaternary Science Review 27, 1583-1599. In the Isbjørnhamna, pockmarks formed on the flat area near the terminal moraine. They are formed after the Little Ice Age and still retreats of Hans Glacier. These pockmarks are concentrated in the western and central part of this flat area. The number of pockmarks on the flat Underwater rocks and skerries- skerries ale located near the coasts, especially at the Wilczekodden and Oseangraftangen. area is 370. The biggest pockmarks are located in the eastern part of this area. The surfaces of pockmarks are between 20 to 340 m2. The Underwater rocks are located on the terminal moraine, too. They form the cluster of rocks. In addition, rock sills separate depths of pockmarks do not exceed 70-80 cm. Samples articles about forms: shallower parts from deeper parts of bays. Forwick M., Baeten N.J., Vorren T.O., 2009, Pockmarks in Spitsbergen fjords, Norwegian Journal of Geology 89, 65-77. Hovland M., Heggland R., Vries M.H., Tjelta T.I., 2012, Unit-pockmarks and their potential significance for predicting flow, Marine and Petroleum Geology 27, 1190- 1199.
Acknowledgement: The work has been partially financed from the funds of the Leading National Research Centre (KNOW) received by the Centre for Polar Studies for the period 2014-2018, project of National Science Centre no. DEC-2013/09/B/ST10/04141 and the statutory activity of the Institute of Geophysics Polish Academy of Sciences.