ABYSSAL DEPTHS


For inquiries contact Ed Klekowski

How deep is the Connecticut River? Would it surprise you to know that in some places its depth exceeds 125 feet? It surprised me.

Two deep sites in Massachusetts are currently being explored by divers. The following map shows their locations; both are near where the French King Bridge spans the Connecticut River. Site B, known as French King Hole, has been dived for years by Valley Divers . The second site, labelled Site A, known as King Philip's Abyss, was recently (summer, 1997) discovered and explored by University of Massachusetts divers. Both sites should be dived with caution: they are very deep, totally without light (dark as the inside of a cow!), have overhangs, and there is the possibility of entanglement from waterlogged, uprooted trees (roots, trunk and crown) that sink to the bottom.

As you will note on the map, both of these deep sites are close to a fault that crosses the Connecticut River. This fault, known as the Border Fault, is worth a geological digression.

Approximately 200 million years ago, all of the continents were united into a single supercontinent called Pangea. Subsequently faults separated the continental plates and they began the slow drift to their present locations. During the initial phase of this continental break up, a fault (the Border Fault) developed through what is now the Connecticut River Valley. This fault aborted, and another occurred east of Boston separating North America from Africa. Had the Border Fault not aborted, Boston would be in Africa and Greenfield, Massachusetts would be a coastal resort! Too Bad.

French King Hole (Site B) exactly coincides with where the Border Fault crosses the river.

THE BORDER FAULT CROSSES THE RIVER IN THE FOREGROUND

UPSTREAM FROM THE FRENCH KING BRIDGE. THE BORDER FAULT IS ON THE RIGHT (EASTERLY) SIDE OF THE RIVER

Faulting may result in neighboring rocks either becoming stronger or weaker. According to Professor Little, a geologist at Greenfield Community College, the rocks in the French King Gorge have been weakened by the Border Fault. Perhaps the 125' depth of this sector of the river is due to the erosion of these fault-weakened rocks by great volumes of water that have flowed through the Gorge in the geological past.

King Philip's Abyss is near the Border Fault, but no known fault crosses the river at this location. The origin of the Abyss is geologically unresolved, but its proximity to the Border Fault is tantalizing.

DIVE FLAG MARKS THE ABYSS

Of the two deep (125 feet plus) river sites, King Philip's Abyss is the more interesting biologically. Therefore our discussion will focus on this habitat. The Abyss is an underwater cliff that crosses the river. The edge of the cliff is 20-30 feet beneath the surface and plunges almost straight down for 80 feet in some locations. The bottom of the cliff is abrupt and then begins an unexplored slope of gravel and boulders going deeper. In some places the cliff is undercut into cavern-like areas.

Since the cliff is in the lee of the flow of the river, this habitat is unique. The cliff wall is festooned with life: white sponges as big as dinner plates and colonies of the bryozoan, Lophopodella carteri, a state listed species, cover the cliff face between the sponges.

SPONGES GROWING ON ABYSSAL WALL. NOTE DIVER'S ARM FOR SCALE.

AND MORE SPONGES!

We as yet know very little about this deep water cliff-face community of invertebrates. During any given dive, because of the depths, only 10-15 minutes are spent sampling for organisms; thus the total diving time actually spent studying this unique environment has probably been less than one hour.

We really don't know what is living down there! This might be the last environment in Massachusetts whose biota is unknown.

References:

Hamblin, W. Kenneth. 1985. The Earth's Dynamic Systems, 4th Edition. Macmillan Publishing Company, New York. See Chapter 22 for a clear discussion of continental drift.

Stopen, Lynne E. 1988. Geometry and deformation history of mylonitic rocks and silicified zones along the Mesozoic Connecticut Valley border fault, western Massachusetts. Master's Thesis, Department of Geology and Geography, University of Massachusetts.