Geology/Hudson River Fjord (?)
I am part of a group of citizens and elected officials who are working to fund the construction of a hiking and biking trail along the Hudson River following Route 9D from Cold Spring, NY to Beacon, NY. This is an are of the Hudson known as the Hudson Highlands. But the project from the beginning has been known as the Hudson Fjord Trail, because the name evokes the juxtaposition of hills, river and riverbed that is known as a fjord: deep riverbed carved by retreating glaciers, wooded hillsides sloping into the river. I've seen the area described as a fjord in some geological literature and our state's Department of Environmental Conservation has referred to the area this way in online material.
Nonetheless, debate continues in our group as to the name's accuracy. My question for you is: In geological terms, is our name for the trail accurate? The name is unique for our area and evocative of the place, but I want to be able to cite expert opinion as to the suitability of the name.
Thank you for your help with this.
Geologically the name is not correct. While it might be evocative of a fjord, the setting is not.
I cite from the glossary of Geology, published by the American Geological Institute.
A) A long narrow winding, U shaped and steep walled generally deep, (often several hundred fathoms)inlet or arm of the sea between high rocky cliffs or slopes along a mountainous coast typically with a shallow sill or threshold of solid rock or earth material submerged near its mouth and becoming deeper far inland; it usually represents the seaward end of a deeply excavaed glacial trough valley that is partially submerged by drowning after the melting of the ice (caps). Examples: along the glaciated coasts of Alaska, Greenland and Norway.
B)Any embayment of the seacoast in a Scandinavian country regardless of the adjacent topography, as a fjard in the low flat Swedish coast or forde in Eastern Denmark.
On the surface, strictly speaking, name fails on numerous accounts.
1) It is not an arm of the sea.
2) 3) It does not bear any of the requisite characteristics imparted by glaciation at all.
4) it is not a drowned glacially incised valley.
What the Hudson Highland Park represents is an water gap. Similar but not as dramatic as the water gap on the Delaware at Harrisburg. A water gap is an indication that the river is older than the surrounding geologic structures. This means the the river was running at a former level above the now existing topography and the ground surface was pushed up, at a slow enough rate that the river cut down through the rocks cutting into the ridges as they were pushed up, or the river let itself down,cutting through the rocks and structures that when they were eroded, became ridges. If the ground surface is pushed up faster than the river can cut, and the river is redirected along the sides of the new water divide, the old gap becomes a "wind" gap, an elevated notch in the ridge. These are seen along the entire Blue Ridge as far south as the Carolinas.
However, I did find a source that claims it IS a fjord as far north as Troy, a stretch I think, but at Cold Spring I think it could be.
The dramatic cliff sides it does not have.
I think you are seeing a water gap, enhanced by glaciation, and the cliffs and high ridges have been removed by the glaciation.
The coast of Norway has little or no continental shelf, the glaciers that covered the land mass, carved valleys into the coast as the ice moved down from the higlands and directly into the ocean, forming submerged hanging valleys. Due to the substantial coastal plain along the east coast, this kind of formation was not possible, but with the drop in sea level, existing rivers like the Hudson cut deeply into the underlying rock as sea level dropped. When sea level rose these deeply excised river channels were flooded.
So I stand by the first strict definition, that a fjord is a drowned valley carved by ice. That may be the case near the mouth of the Hudson, but not as far north as Troy. The other source cites the deepness of the channel, but as I pointed out, this could have been caused by the drop in sea level. One way to determine if the area you are concerned with was glacially carved would be to obtain a profile of the river channel to see if it bears the characterisitc U shape of a glacially carved valley.