The glacial landforms and sediments of Interstate Park were largely created during the retreat of the Superior Lobe from this region and periodic outburst flood events from proglacial lakes, e.g. Lake Duluth, since the Last Glacial Maximum. First, the retreat of the Superior lobe into the Lake Superior basin created proglacial lakes. Initially, these lakes consisted of small, proglacial lakes. Later, these lakes coalesced to form a large proglacial lake called glacial Lake Duluth, which was confined to the western Superior basin. The most prominent of multiple lake levels of glacial Lake Duluth is known as the Duluth level. There also was an older epi-Duluth level that lay above the Duluth level. The epi-Duluth level and a smaller precursor proglacial lake, named Lake Nemadji, drained through the higher Moose Lake (Portage) outlet into the Kettle River and into the St. Croix River. As the Lake Superior Lobe retreated, the Brule outlet opened and the higher Moose Lake was abandoned as a lower Duluth level was quickly established by massive and sudden outflow through the lower Brule outlet and down St. Croix River. The Brule outlet was abandoned when Lake Superior Lobe retreated from the Keweenaw Peninsula and opened lower eastward draining outlets. This caused the Duluth level to drop abruptly to post-Duluth levels and water to cease flowing into lower Brule outlet and down the St. Croix River.