pwhole
Well-known member
As part of a long-term private research project into the lava bodies around Castleton in the Peak District - essentially belonging to geologist Mark Harwood (though I've managed to elbow my way in over the last few years by doing underground work he can't do) - we've been logging the various outcrops, both above and below ground, to try and add a bit more caver-related information to the geological records that already exist. To that end, we did a lot of subsurface geophysics scanning of the Speedwell Vent a few years ago (documented in TSG 19, and also expanded for a MSc Thesis soon after), and we've been resurveying and sampling in mines known to contain outcrops - mainly the tuff in Pindale End mine, but also a bed of the Lower Millers Dale Lava seen 25m down Hazard engine shaft. We've recently found a new, completely undocumented occurrence of lava/tuff, which will be documented soon.
The Cavedale Lava is particularly interesting as it sits above a large chunk of Peak Cavern, and although the 'umbrella' effect of the lava is well-known, in terms of preventing formations from growing beneath it, less has been written about the formation of the cave itself beneath the lava. As the White River bedding is not far below the horizon of the lava, and the deep shaft of Victoria Aven and the top of George Cooper Aven both break into a lava choke at the very top, it's likely that the lava bed (or breaches in it) strongly influenced the development of the cave below - this may have occurred synchronously with the downcutting of Cave Dale itself. The lava outcrop as mapped by the BGS is an unusual shape, and as far as we can tell hasn't been verified by any underground testing from the surface. To that end we revisited the area in February to make a full inspection of all the visible outcrops, and I offered to gather underground samples wherever possible.
Echo Chamber, reached by climbing Victoria Aven and then descending George Cooper Aven from the Victoria Line trunk passage, has a large collection of lava pieces at the base of the first main slope - one is a cubic metre in dimension, and may be part of a hexagonal column - but there are many small pieces scattered around, and so on a recent trip I grabbed a few samples, which are shown below. Quite a variety of types, but my knowledge of this stuff is limited, so they'll be sent over to Mark for analysis soon. But three out of four are vesicular, whereas the fourth is more of a tuff, with some pretty green crystals scattered throughout. I'll reserve my judgement any further at the moment, but they look very nice
These have clearly been washed down the cave system from the outcrop high above, most likely in the vadose phase when the various breaches of the White River bedding were occurring, but that's as much as I know so far. Unless anyone else knows more! I've read all the geological memoirs.
A QGIS render below shows the Cavedale Lava outcrop in pink, with some of the Peak Cavern survey beneath in red.
The Cavedale Lava is particularly interesting as it sits above a large chunk of Peak Cavern, and although the 'umbrella' effect of the lava is well-known, in terms of preventing formations from growing beneath it, less has been written about the formation of the cave itself beneath the lava. As the White River bedding is not far below the horizon of the lava, and the deep shaft of Victoria Aven and the top of George Cooper Aven both break into a lava choke at the very top, it's likely that the lava bed (or breaches in it) strongly influenced the development of the cave below - this may have occurred synchronously with the downcutting of Cave Dale itself. The lava outcrop as mapped by the BGS is an unusual shape, and as far as we can tell hasn't been verified by any underground testing from the surface. To that end we revisited the area in February to make a full inspection of all the visible outcrops, and I offered to gather underground samples wherever possible.
Echo Chamber, reached by climbing Victoria Aven and then descending George Cooper Aven from the Victoria Line trunk passage, has a large collection of lava pieces at the base of the first main slope - one is a cubic metre in dimension, and may be part of a hexagonal column - but there are many small pieces scattered around, and so on a recent trip I grabbed a few samples, which are shown below. Quite a variety of types, but my knowledge of this stuff is limited, so they'll be sent over to Mark for analysis soon. But three out of four are vesicular, whereas the fourth is more of a tuff, with some pretty green crystals scattered throughout. I'll reserve my judgement any further at the moment, but they look very nice
These have clearly been washed down the cave system from the outcrop high above, most likely in the vadose phase when the various breaches of the White River bedding were occurring, but that's as much as I know so far. Unless anyone else knows more! I've read all the geological memoirs.
A QGIS render below shows the Cavedale Lava outcrop in pink, with some of the Peak Cavern survey beneath in red.
