Tallest peak and lowest valley?

[Jimjam]

Could be both were tarns, turned lakes, but silted up after the ice retreated. The earthworks of creating a large city caused a compacting or other interruption of the silt in what was to become the LOIO, which then displaced groundwater, causing it to rise up from the spring that feed the water that ended up on top of the lake and flowing down into the sea by the port.