Deglaciation of the Northwestern White Mountains, New Hampshire
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Géographie physique et Quaternaire, 1999, vol. 53, n° 1, p. 59-77, 14 fig., 3 tabl. DEGLACIATION OF THE NORTHWESTERN WHITE MOUNTAINS, NEW HAMPSHIRE Woodrow B. THOMPSON*, Brian K. FOWLER** and Christopher C. DORION***, respectively Maine Geological Survey, 22 State House Station, Augusta, Maine 04333-0022 U.S.A.; Mount. Washington Observatory, P. O. Box 2310, North Conway, New Hampshire 03860 U.S.A. and Geological Services, 79 Bennoch Rd., Orono, Maine 04473 U.S.A. , 1999, vol. 53, n° 1, 14 fig., 3 tabl., 53(1), 1999W. B. THOMPSON, B. K. FOWLER and C. C. DORION ABSTRACT The mode of deglaciation in the RÉSUMÉ La déglaciation du nord-ouest des ZUSAMMENFASSUNG Enteisung der nord- northwestern White Mountains of New Hamp- White Mountains, au New Hampshire (E.- westlichen White Mountains, New Hampshire. shire has been controversial since the mid U.A.). Le mode de déglaciation du nord-ouest Die Art des Abschmelzens in den nordwestli- 1800’s. Early workers believed that active ice des White Mountains a fait l’objet de contro- chen White Mountains von New Hampshire ist deposited the Bethlehem Moraine complex in verses depuis le milieu du XIXe siècle. Les pre- seit Mitte des 19. Jahrhunderts umstritten ge- the Ammonoosuc River basin during reces- miers chercheurs ont supposé que le wesen. Die ersten Forscher glaubten, dass ak- sion of the last ice sheet. In the 1930’s this de- complexe morainique de Bethlehem dans le tives Eis die Bethlehem-Moräne-Einheit glaciation model was replaced by the concept bassin de l’Ammonoosuc River avait été mis während des Rückzugs der letzten Eisdecke im of widespread simultaneous stagnation and en place par la glace active au cours du recul Becken des Ammonoosuc-Flusses ablagerte. downwastage of Late Wisconsinan ice. The du dernier Inlandsis. Au cours des années In den 30er Jahren des 20. Jahrhunderts wurde present authors reexamined the Bethlehem 1930, ce modèle de déglaciation a été rempla- dieses Enteisungsmodell durch das Konzept Moraine complex and support the original in- cé par le concept selon lequel il y aurait eu sta- einer gleichzeitigen weitflächigen Stagnation terpretation of a series of moraines deposited gnation simultanée sur une grande étendue et und Abwärtszehrung des Spät-Wisconsin-Ei- by active ice. We found other moraine clusters fonte de l’inlandsis du Wisconsinien supérieur. ses ersetzt. Die gegenwärtigen Autoren haben of similar age to the northeast in the Johns Riv- Les présents auteurs ont réétudié la Moraine die Bethlehem-Moräne-Einheit neu untersucht er and Israel River basins. Ice-marginal depos- de Bethlehem et appuient l’interprétation ori- und stützen die ursprüngliche Interpretation ei- its that probably correlate with the Bethlehem ginelle selon laquelle il s’agit d’un ensemble de ner Serie von Moränen, welche durch das akti- Moraine also occur west of Littleton. The Be- moraines terminales mises en place par une ve Eis abgelagert wurden. Sie fanden weitere thlehem Moraine complex and equivalent de- Moränen-Einheiten ähnlichen Alters nordost- glace active. Ils ont aussi découvert d’autres posits in adjacent areas were formed by wärts in den Becken von Johns River und Israel ensembles morainiques d’âge similaire au readvance and oscillatory retreat of the Con- River. Eisrand-Ablagerungen, die wahrschein- nord-est, dans les bassins de Johns River et necticut Valley lobe of the Laurentide Ice lich mit der Bethlehem-Moräne korrelieren, tre- Israel River. Quelques dépôts de marge gla- Sheet. This event is called the Littleton-Beth- ten auch westlich von Littleton auf. Die ciaire, probablement de la même époque que lehem Readvance. Throughout the study ar- Bethlehem-Moräne-Einheit und entsprechen- celle du complexe morainique de Bethlehem, ea, sequences of glaciolacustrine deposits de Ablagerungen in angrenzenden Gebieten ont aussi été identifiés à l’ouest de Littleton. Le and meltwater drainage channels indicate pro- wurden durch Rückvorstoβ und oszillatori- complexe morainique de Bethlehem et les dé- gressive northward recession of the glacier schen Rückzug der Connecticut Tal-Lobe der pôts équivalents dans les zones adjacentes margin. Radiocarbon dates from nearby New laurentischen Eisdecke gebildet. Dies Ereignis ont été mis en place par récurrence et retrait England and Québec suggest that the ice nennt man den Littleton-Bethlehem-Rückvor- sheet withdrew from this part of the White oscillatoire du lobe de la vallée du Connecticut stoβ. Durch das ganze erforschte Gebiet hin- Mountains between about 12,500 and appartenant à l’Inlandsis laurentidien. Il s’agit durch weisen Folgen glaziallimnischer 12,000 14C yr BP. We attribute the Littleton- de la récurrence de Littleton-Bethlehem. Les Ablagerungen und Schmelzwasser-Drainage- Bethlehem Readvance to a brief climatic cool- dates obtenues en Nouvelle-Angletterre et Rinnen auf einen Rückzug des Gletscherrands ing during Older Dyas time, close to dans le Québec limitrophe laissent supposer in Richtung Nordwest. Radiokarbondaten vom 12,000 BP. que l’Inlandsis laurentidien s’est retiré de cette nahen Neu-England und Québec legen nahe, partie des White Mountains vers dass die Eisdecke sich von diesem Teil der 14 12 500-12 000 C BP. Les auteurs attri- White Mountains zwischen etwa buent la récurrence à une refroidissement cli- 12 500-12 000 14C Jahren v.u.Z. zurückzog. matique de courte durée vers 12 000 BP, Wir schreiben den Littleton-Bethlehem Rück- pendant le Dryas ancien. vorstoβ einer kurzen Klima-Abkühlung wäh- rend des älteren Dryas zu, um 12 000 v.u.Z. Manuscrit reçu le 22 mai 1998 ; manuscrit révisé accepté le 14 décembre 1999 * E-mail address: [email protected] ** E-mail address: [email protected] *** E-mail address: [email protected] 60 W. B. THOMPSON, B. K. FOWLER and C. C. DORION INTRODUCTION sustained glacial flow (e.g. Gerath, 1978; Gerath et al., 1985; and Thompson and Fowler, 1989). Many geologists have investigated the glacial history of the White Mountains (see historical review by W. B. Thomp- The present study reexamines the Bethlehem Moraine complex, which is a belt of linear and hummocky glacial son, this volume). The early visits of Louis Agassiz, Edward deposits in the towns of Bethlehem and Littleton. This com- Hitchcock, and Charles Lyell stimulated interest in the plex was at the center of debate over the mode of deglacia- region. Studies in the northwestern White Mountains, tion in the White Mountains, having been used by between the Presidential Range and the Connecticut River, proponents of both active-ice and stagnation retreat to sup- led to controversy over the relative importance of local port their views. We also investigated other deposits to the (alpine) versus continental glaciation in this part of New east and west that may have formed at the same time as the Hampshire (Goldthwait, 1916). Later debate concerned the moraines in Bethlehem and Littleton. These include a thick style of deglaciation—whether there was active-ice retreat or section of glacial sediments next to Comerford Dam in the wholesale stagnation and accompanying downwastage of Connecticut River valley, which previous workers have the ice sheet (Goldthwait, 1938; Lougee, 1940). The concept attempted to correlate with the Bethlehem Moraine. of stagnation and downwastage in New England was domi- The Bethlehem Moraine complex is located in the central nant from the 1930’s until the late 1900’s. Ammonoosuc River basin. This river originates on the side of The application of the morphosequence concept in cen- Mount Washington in the Presidential Range and flows west to Littleton, whence it takes a southwesterly course to the tral to southern New England (Koteff and Pessl, 1981) Connecticut River (Fig. 1). The deglaciation history of the showed that systematic ice-margin retreat occurred in many Ammonoosuc basin is closely related to that of neighboring areas where end moraines are scarce or absent. This para- river basins to the north. The Israel River drains part of the digm shift forced a reevaluation of the stagnation theory northern Presidential Range and flows northwest to the Con- throughout the region. Recent descriptions of moraines and necticut River at Lancaster. Between the Ammonoosuc and glaciotectonic structures in the northeastern White Moun- Israel Rivers is the Johns River, a shorter stream that flows tains have shown that active ice persisted during deglacia- northwest through Whitefield and enters the Connecticut tion in areas that were topographically favorable for River in Dalton (Fig. 1). FIGURE 1. Map of northern White Mountain region, showing principal Région du nord des White Mountains, montrant les principales villes towns and rivers in New Hampshire and adjacent Vermont. Thick gray et rivières du New Hampshire et du Vermont attenant. Le trait gris large line is inferred southern limit of Littleton-Bethlehem Readvance. marque la limite méridionale de la récurrence de Lettleton-Bethlehem. Géographie physique et Quaternaire, 53(1), 1999 DEGLACIATION OF THE NORTHWESTERN WHITE MOUNTAINS 61 Damming of the west-draining Ammonoosuc, Israel, and mountains after recession of the continental ice sheet. Upham Johns River valleys by the receding Late Wisconsinan ice could not distinguish the sharp moraine ridges reported by sheet formed a series of ephemeral lakes (Lougee, n.d., Agassiz, and he characterized the Bethlehem Moraine as 1939). Northward recession of the ice sheet opened pro- being the “continental type”. Upham’s description is close to gressively lower outlets for these lakes. We used the posi- what the present authors have seen: “The material of this belt tions and elevations of the spillway channels, together with is chiefly till, with some modified drift, as kames, or knolls of moraines and ice-contact deltas, to help reconstruct the gravel and sand. The contour is very irregular, in multitudes of sequence of deglaciation. hillocks and little ridges, grouped without order or much paral- lelism of their trends. Everywhere in and upon these deposits PREVIOUS WORK boulders abound,..