[Journal entry for February 2, 2008]. Today is a bit brighter than yesterday, with its heavy rains, but is still rather cloudy. I am visiting the tension cracks along the Hudson Palisades cliffs that are south of State Line Lookout. I have walked past them many times since noticing them for the first time more than a decade ago, but I have never really given them a close look.

I park at the Lookout and take the Long Path southward, along the edge of the cliff. According to a sign, the cliff is 532 feet high in this area. The trail first descends down into a deep gulley – a cleft in the cliff that reaches about half way down. I follow a well-engineered rocky staircase down the north side. I pass a very impressive rock spire, a big polygonal column of basalt. I then cross a little brook at the bottom of the gulley. Overhanging banks with dangling tree roots suggest that rapid erosion has been occurring here. I then huff back up to the cliff top. I pass the Federation Memorial Tower. It’s a small stone structure with a plaque that describes it as commemorating the efforts of Women’s Clubs in preserving the park. I leave the Long Path, which turns a bit to the west, and follow the trail that is closest to the cliff’s edge.

Crack System 1. The first of the cracks is located just a little past the tower. It’s a narrow feature and easily missed if your attention is focused on the spectacular river view that’s on the other side of the trail. Perhaps that’s why it’s enclosed by a now-ancient and dilapidated green guardrail. A fall into the crack easily could be fatal. It has steep sides and in some places is ten feet deep. Looking around, I find a few dark crevices that extend further down another ten feet or more. The general area actually has two cracks. The second is to the west of the first and not as well-developed, or at least no rock faces are exposed on the earth’s surface. The crack is recognizable mainly from the sag in the land. These two sub-parallel cracks are each about a hundred yards long, and parallel the edge of the cliff.

This area must have been the site of an old habitation. One depression in the ground is lined by blue tile – the remains of an old swimming pool. And the vegetation includes some hedges, that while now untrimmed and growing wild, nevertheless look very much out of place.

The tension cracks are indistinguishable from the many similar cracks that I have seen on the volcanic island of Iceland during my years of geophysical exploration. All these cracks have near-vertical sides and are partly filled by blocky chucks of rock that have fallen out of their sides. At the small scale, the crack follows natural joints between these blocks, suggesting that the cracking process did not break the individual pieces so much as pull them apart from one another. Both the Palisades and Iceland cracks are basalt, a volcanic rock known for its tendency to develop intense jointing. The tensional forces are probably similar too, despite having different causes, tectonic motions in the case of Iceland and gravity slowly pulling down the cliff, in the case of the Palisades.

Crack System 2. I continue along the trail to the second crack. It’s much larger than the first, a steep-sided gorge or chasm, twenty or thirty feet deep and a hundred feet wide, with a small stream flowing down its middle. Unlike the first set of cracks, which are wholly within the material of the cliff, this one intersects the cliff edge. I spot one area along the northwestern side of the chasm where some recent displacement has occurred. A small subsidiary crack has recently opened, separating a small slice of rock from its connection with the chasm’s side. A sloping pile of soil on the top of the slice indicates that this crack opened rather recently, probably this year. The crack appears deep, but whether it extends beneath the level of the stream is unclear to me.

I am, of course, interested in knowing whether these cracks have had any recent activity. Certainly the guard rail suggests that they are old features that predate the building of the Park in the nineteen-thirties. Perhaps they date to the end of the Ice Age, and were caused by the unloading of the Hudson Valley when the glacier that one filled it melted, fifteen thousand or so years ago. Or perhaps they are more recent. The new chasm-edge crack is suggestive of some recent action, but not definitively, since it is unclear whether it represents widening of the overall structure or merely the slumping of the edges of the existing, larger crack. However, over the years I have seen many small rock falls from the Palisades Cliff. It’s only a matter of time before a really large chunk goes.

I walk down into the chasm, following the stream, being on guard all the time for the possibility of hard-to-see and very hazardous cracks at its bottom. I do indeed find one of these, on the southern side of the chasm up against a vertical rock wall. It’s a sink hole about a yard wide that extends down into the earth to a depth of at least twenty feet. A little water is dripping into it, and I can hear more water gurgling at depth. I soon discover that the stream that I have been following does not run the full length of the chasm and so does not create a waterfall at the cliff edge. Instead, with no drama, it simply ends in a damp patch of old leaves. I presume that another sink hole lurks under those leaves, but I fear to get to close.

I return to the cliff top and walk to the little rocky point of land, just south of the intersection of the chasm with the cliff edge. It affords a nice view of the Hudson, as well as the chasm. Despite the rain, some ice still clings to the cliff in the shadowed corner.

Crack System 3. The cliff edge trail rejoins the Long Path south of the chasm and itself now runs along the cliff edge. I follow it to where it crosses a small stream. Unfortunately, the ford has been blocked by the fall of a large tree. The new ford has fewer stepping stones and is harder to cross than the old one. I notice, for the first, time that this stream is itself flowing in a shallow trough might well be another tension crack. I follow the stream south, and sure enough, it disappears in another patch of leaves and sand. The region of this sink hole has some nearby bedrock that I can stand safely on, so I approach cautiously and poke a long stick down into the debris. The stack sinks easily to the depth of a foot or so, like in quicksand, but does not break through to any sort of cavity. The trough develops into a well-defined tension crack south of this sinkhole – one with steep sides and piles of angular blocks. This well defined crack peters out again into a shallow trough, which goes on to intersect the cliff-edge. Overall, this crack is several hundred yards long.

The Long Path crosses several more streams. One crossing is via a fairly well-built foot bridge across a narrow but section of stream. I think that the stream bed in this are is not natural, but rather has been specifically engineered to create a waterfall in a carefully chosen section of the cliff edge. I any case, the waterfall there is quite lively and picturesque – thanks to yesterday’s rain.

Crack System 4. I walk another half-mile south on the Long Path to the last of the crack systems (or at least, the last of the ones that I know about). It is another wide and deep chasm that is set very close to the cliff edge. It is spanned by a sturdy steel footbridge. I cross it and stand atop the rather thin stone sliver that makes the eastern wall of the chasm. The sliver is not so narrow to be especially dangerous. It’s at least five feet wide even at its narrowest, and in most places is more like ten or twenty. But it’s still daunting to stand in such an exposed place. The Palisades Cliffs are themselves very vertical at this spot, and very high. One deep sinkhole is visible in the chasm itself, towards its southern end – dark and of unknown depth.

I return to State Line Lookout, mostly using the Long Path, but taking a diversion to the west just south of Federation Memorial Tower, so as to be able to loop around the big gulley, rather than climb down into and up out of it again. I’ve hiked at a leisurely pace today. The overall trip took about two and a half hours.