Discover the forest primeval at Odiornes Point

It reminds us that the landscape is not static

Jim Cerny, story and photography

Remains of drowned (submerged) forests are found along the coastline from New Hampshire to Nova Scotia. They are typically radiocarbon dated to about 4200-3000 years before present (BP). They drowned because sea level has continued to rise relative to the land with the melting of the ice sheet that once covered the area 14,000 years BP. The forest remains can be seen when protective overlying sand or cobbles are removed in storms and the tide is low. Sometimes these are incorrectly called petrified forests, which are a totally different phenomenon, involving the mineralization of wood.

Odiorne drowned forest.

The Odiorne stumps (and logs) are covered in the booklet "The Geology of the Seacoast Region, New Hampshire," by Robert Novotny (1969), describing exactly how they looked on the morning I took the accompanying photographs:
At times of very low tide the floor of the cove is exposed. It consists of patches of cobbles, pebbles and sand alternating with shallow tidal pools. Here and there the lower portion of a heavy stump may be seen. These are not conspicuous as they have been ground off level with the cove floor by rock fragments which have been dragged back and forth by wave action.  Occasionally a whorl of heavy roots may be seen surrounding a stump. [p. 3]
It is not clear how often these forest remains are uncovered and can be seen. My visit was after the fierce storm at the end of February on a -0.1 foot low tide and low tides can be even lower at the full moon as much as -1.6 feet can occur.

Drowned forest as seen from Ocean Boulevard (Rte. 1A) looking directly out to sea to the east. Appledore Island is on the horizon at the extreme right. This is at low tide with the stumps partly exposed and partly covered by the residual pool of water.

Diagram view of Odiorne drowned forest. (used with permission from Harrison and Lyon, "Journal of Geology," January 1963, pp. 96-108, fig. 2). Note that this is oriented with north at the top.

Same orientation as first picture, but standing among the cobbles, nearer to the tidal pool (click on image for larger view). To see the stumps and logs you have to be nearly on top of each one.

The view when standing among the stumps of the drowned forest and looking westward toward route 1A (Ocean Boulevard). The white box shows a stump among the cobbles click on it to see a detailed view. Many stumps are less noticeable than this one.

Drowned forest stump with surrounding whorl of roots (with dollar shown for scale). A number of the more easily recognized stumps look like this.

Between a scientific study of the Odiorne drowned forest in 1934 and a more detailed study and dating in 1963, there has been noticeable erosion of the stumps. This suggests the stumps have not been exposed since they drowned. A likely explanation is that they have been covered by beach deposits and as the beach berm has shifted landward, it has exposed the forest in relatively recent times. And in this location the stone cobbles and offshore ledges provide some additional protection.

The 1963 study determined that the stumps are rooted in woodland peat that is 2.5 to 4.0 feet thick. White pine, hemlock, and maple species have been identified, but radiocarbon dating was limited to pine samples. The samples date from about 4200 years BP to 3200 years BP. While it is possible that the trees were killed in a complex series of ocean advances and retreats, the scientists concluded it was more likely to be drowning by a gradual advance, estimated at 1.1 feet per century in the middle of that time period.

Another stump typical of those with a whorl of roots.

Fallen log, out of water click to see larger view.

Fallen log, in a tidal pool click to see larger view.

Drowned forest stump or log, unusual in showing so much grain detail.

The geologic history.

The sequence of post-glacial sea level changes is well documented for the State of Maine and we can reasonably extrapolate from that for New Hampshire. The maximum extent of the last glaciation was about 14,000 years BP. At that time sea level was far to the east, but the land in the Seacoast was depressed by the weight of the ice and was actually below that sea level. As the ice rapidly melted and raised world-wide (eustatic) sea level, the land also started to rebound from the removal of the weight of all that ice (isostatic rebound), but at first sea level rise outpaced land rebound. At one time around 10,000 years BP the sea extended inland as far as the Lee traffic circle and left beach deposits on the side of glacially shaped hills (drumlins) like Stratham Hill. During this time thick deposits of marine clay also formed in many areas, which were once the basis of brick kilns in towns surrounding Great Bay. Eventually the land rebounded to the point where it was above present day sea level, allowing forests and woodland peat to form, more than 4000 years BP. Since that time sea level has continued to slowly rise, drowning the forests.

Radiocarbon dating methods were not available when the drowned forests were first noted and studied. Radiocarbon dating puts the middle date of the Odiorne forest at about 3600 BP. When plant material is formed it contains a mix of three isotopes of carbon, one of which is radioactive (carbon-14 or 14C) and decays at a predictable rate (the half-life). Based on the amount found remaining in a sample, it is possible to estimate the amount of time it would take for an original quantity to leave that remainder, giving the date when the sample died. This works for samples not more than 60,000 years old. Researchers took four samples from pine stumps at Odiorne, careful to use outer layers (last growth) and to avoid contamination with current marine life, plus they applied the Suess correction to allow for changes in the carbon isotope ratios since industrialization began.

We live in the landscape left by the most recent in a series of glaciations over the last two million years, with the last four glaciations having a cycle of about 100,000 years of ice advance and about 10,000 years as an interglacial period. Undoubtedly drowned forests have been created and destroyed during each cycle whether the next cycle will take place or be disrupted by human activity remains an open, long term question!


April, 2010