Interpretación y cartografía de paleolíneas de costa lacustres mediante fotografías aéreas de alta resolución y datos LiDAR en la laguna de Gallocanta (NE España)

Abstract

Gallocanta Lake, with and extension of 14 km 2 , is located between Zaragoza and Teruel provinces. It experiences frequent water level fluctuations, oscillating between total desiccation and 3 m of maximum depth. The lake is exposed to strong persistent winds blowing from the NW, which generate waves, currents and sediment transport along the shores, where beaches, spits, ridges and other coastal forms are common. The recognition of ancient, Upper Pleistocene, littoral ridges in quarries located in the perilacustrine zone suggests a much greater extension of the lacustrine environment in past times, reaching at least 45 km 2 of water surface, at a height more than 15 m above the present lake bottom. Flat surfaces existing between such ridges and the present lake include morphosedimentary records of palaeoshorelines formed in Holocene and historical times. Given the difficulty of recognition of such relict forms by using traditional methods, two alternative sources of information were employed: high-resolution aerial photographs (1:15.000) and a digital terrain model generated from LiDAR data with 0.2 m resolution. Topography was analysed in a continuous way extracting contour lines in order to obtain a high-resolution topographical interpretation. The results were later integrated in a SIG environment, together with field inspection. As a result, a series of stepped relict littoral form sequences have been obtained, completely surrounding the present lake, with a great lateral continuity. About 10 different relict levels have been identified, some of them hosting spectacular well preserved littoral forms like spits with recurved hooks, counter-spits, bays closed by barrier islands, parallel bar systems, palaeodeltas, etc. All these forms allow a preliminary reconstruction of the littoral dynamics prevailing in the past on the lake shores.

Water level control on coastal landform distribution and associated processes in a highly fluctuating shallow lake (Gallocanta Lake, NE Spain)

“…In Gallocanta Lake, the maximum effective fetch was calculated in a previous work (Gracia, 1995) According to the morpho-sedimentary records of past stages (Gracia et al, 2021), Gallocanta Lake very likely began to develop in the Late Pleistocene already as a wind-driven lake. Following the reconstruction of its initial morphology made by Gracia and Castañeda (2018), who used the location of the oldest littoral ridges preserved in the SE zone (see Figure 1) as topographic reference, the original lake was about 4 km longer than at present, with a depth of 18 m. The resulting I WWB index would be around 15, still entering into such category. The later progressive aridification trend during the Holocene (Luz on et al, 2007) and the present situation of increasing aridity are making the lake acquire a typical character of fully wind-driven waterbody.…”

Water Level Fluctuations in Gallocanta Lake (Spain) Using Sentinel-2 Remote Sensing

“…It has a maximum capacity of 5 hm 3 and an average depth of 45-50 cm, although it can reach 3 meters in the high-water season. (Comín, et al, 1991;Velasco, 2006;Arnaiz, 2013;Gracia and Castañeda, 2018). Its basin is between a minimum and maximum altitude of 995 meters and 1085 meters, respectively (Government of Aragon, 2020).…”

“…Maximum rainfall occurs between the months of May and June, while minimum rainfall occurs in the months of July, August, January and February. As for the precipitations, they are around 500 mm, with a wide pluviometric variation, which produces fluctuations in the water level between total desiccation and almost 3 meters deep (Gracia and Castañeda, 2018). While the average annual temperature is 10.7 ºC, the maximum monthly average recorded in July is 21.1 ºC and the minimum in January is 2.9 ºC.…”