Deglaciation of Penobscot Bay, Maine, USA


  • Emmy A. Wrobleski School of Earth and Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA
  • Roger LeBaron Hooke School of Earth and Climate Sciences and Climate Change Institute, University of Maine, Orono, Maine 04469, USA



The Pond Ridge and Pineo Ridge moraines in downeast Maine likely formed at ~16.1 and ~15.7 ka respectively, during cold episodes recorded by δ18O dips in the GRIP ice core. The elapsed time between these ages is broadly consistent with retreat rates recorded by intervening De Geer moraines, which are readily visible on LiDAR imagery and are believed to be approximately annual. North-northwestward from the southwesterly extension of the Pond Ridge moraine there are three pairs of prominent moraines that are relatively continuous across the study area and could be reliably extrapolated across intervening water bodies. Retreat rates recorded by De Geer moraines suggest that these pairs formed at 15.7-15.8 ka, 15.5-15.6 ka, and ~15.5 ka. Although retreat appears to have occurred slightly faster across Penobscot Bay, a significant calving bay does not seem to have developed there. Instead, the ice margin remained relatively straight, retreating to the north-northwest. De Geer moraines become more widely spaced northward and vanish after ~15.5 ka when the ice margin was north of the head of Penobscot Bay and of Pineo Ridge. This likely reflects higher retreat rates during the initial phases of the Bølling warm period. Just south of Pineo Ridge there were two ice lobes; one retreated to the north and one to the northwest. The latter retreated more rapidly, while the former experienced numerous minor readvances and stillstands until finally pausing at the location of Pineo Ridge. A stillstand of this lobe then resulted in deposition of the Pineo Ridge moraine complex.

Author Biography

Roger LeBaron Hooke, School of Earth and Climate Sciences and Climate Change Institute, University of Maine, Orono, Maine 04469, USA

Research Professor

I retired from the University of Minnesota in 1999, but am still actively engaged in research and some teaching.

I copied and pasted my ORCHID number from ORCHID, but you say it is invalid.




How to Cite

Wrobleski, E. A., & Hooke, R. L. (2020). Deglaciation of Penobscot Bay, Maine, USA. Atlantic Geology, 56, 147–161.