Interlobate eskers are the largest esker landforms in Finland. They formed in complex depositional conditions during the deglaciation of the Scandinavian ice sheet ca. 10 000 years ago. Their deposits can be 100 m thick, and they consist of high variety of sedimentary structures in large-scale depositional units. The significance of these large landforms to society is great as they host significant groundwater resources and sand and gravel deposits. In addition to protective legal procedures, thorough research and understanding of esker characteristics and groundwater conditions is vital for the sustainable use of eskers. The key to esker characterization is the use of a sedimentological approach for the recognition of the sedimentary structures and for the interpretation of the depositional conditions which formed the esker, as well as geophysical methods with adequate depth penetration. The combination of these two methods allows the characterization of large-scale architectural esker elements such as the coarse-grained esker core, overlapping esker fans and deformation structures (MUKHs) which form the basic hydrogeological units of the eskers. The reliable locating of these elements influencing the groundwater flow is essential in terms of groundwater utilization. In addition, knowledge on bedrock level and the variations in bedrock topography are needed to obtain the correct thickness of the esker deposits. 

The detailed sedimentological characterization of the Lohtaja-Kivijärvi esker revealed a new type of esker formed between two ice lobes, an ice-lobe margin esker. In the case of this esker, the interlobate environment was altered by the readvance of the neighboring ice lobe, and therefore this esker is not purely an interlobate esker. This esker challenges the assumption of thick and extensive eskers being formed between two ice lobes due to its modest extent and thickness. In addition, its depositional characteristics revealed changes in the ice dynamics as well as in the meltwater flow patterns. Researching thick interlobate esker deposits down to the bedrock level has not succeeded so far because the depth penetration of the available geophysical methods in Finland has not been adequate. The results of the first landstreamer-based high resolution seismic reflection pilot surveys in Finland on complex and thick interlobate esker deposits are represented. The results show the applicability of the landstreamer-based high-resolution seismic reflection method in the characterization of the interlobate esker architectural elements and bedrock level and topography variation. The combined use of the sedimentological approach and geophysical methods (ground penetrating radar and high-resolution seismic reflection) is recommended for the comprehensive understanding of thick and complex interlobate esker deposits and in the future potentially for large ice-marginal landforms like the Salpausselkäs.