To begin initiation of a drilled pothole some imperfection at the surface must first be present to allow the drilling to get started. Joint cracks and other rock disintegration provide imperfections. Plucking of rock material is one way a pothole is set up for later drilling. Strong turbulent flow of flood waters will pluck loose rock and create vortices that can drill thru rock.
Click a link to see original photos
From left to right: note the joint line (crack) bisecting this pothole – this could have been the imperfection needed to start the plucking and later hydraulic drilling that created this pothole Jacob's Well - Wimberley, Texas - a still submerged pothole; Side-breached pothole of the Lower Susquehanna River; Side-breached pothole of the Lower Susquehanna River
From left to right: Susquehanna River, N Y state – small diameter potholes are next to a larger pothole showing multiple vortices may have been present at the time these were drilled; reconstruction of an eroded/broken pothole - St Croix River, border of Minnesota and Wisconsin; Pothole at Hilton Falls, Ontario
From left to right: Kaunertal Valley pothole, Austrian Alps; St Croix River Pothole, Wisconsin-Minnesota border - 12-15 feet wide - 60 feet deep; looking up out of a pothole on St Croix River - Minnesota-Wisconsin border
From left to right: Vortex in draining bottle of water. -To drill a deep narrow pothole a vortex must occur. Vortices are common in the turbulent flow of flood waters; St Croix River, Minnesota – the deepest portion of this pothole has a narrow diameter – this is in accord with the manner of the vortex drilling – watch the animation below to see how the most drilling occurs in the center of the hole closest to the vortex axis of rotation/
Snip from http://en.wikipedia.org/wiki/Vortex : …Vortices are a major component of turbulent flow. In the absence of external forces, viscous friction within the fluid tends to organize the flow into a collection of so-called irrotational vortices. Within such a vortex, the fluid's velocity is greatest next to the imaginary axis, and decreases in inverse proportion to the distance from it. The vorticity (the curl of the fluid's velocity) is very high in a core region surrounding the axis, and nearly zero in the rest of the vortex; while the pressure drops sharply as one approaches that region
From left to right: The 'Eagle's Nest' is a cluster of potholes containing some large rounded boulders, located in the cliffs of the Niagara Escarpment overlook...; Rovaniemi, Finland – this pothole must have had several different flood events to cause this pattern
Irrotational Vortex Flow
From left to right: IrrotationalVortexFlow – click on the picture for animation - this is how a pothole gets drilled deeper than wide – the strongest drilling occurs closest to the rotational axis of the vortex where the rotation is the fastest; Fossil Falls, Coso Range, CA - this pothole appears to have rotational drill marks in the rock; Ruby Falls in Chattanooga--an amazing underground cave waterfall. This is a karst region but some holes like this may have started as potholes – while disintegration of the rock below the surface was taking place there may have also been conditions at the surface creating a pothole
A visit to the inter-mountain waterfalls of Trummelbach in the Lauterbrunnen Valley, Switzerland will show the power of water vortices to carve rock and drill potholes.
14 minute video of a trip inside the mountain at Trummelbach Falls
Published on Jul 22, 2012
The Trümmelbach Falls are the world's only glacier waterfalls that are accessible underground by lift, galleries, tunnels, paths and platforms. They alone carry the meltwater of the glaciers from the Jungfrau down to the valley - up to 20,000 liters of water per second. The water carries with it over 20,000 tons of boulders and scree per year and causes the entire mountain to shudder and make a thundering noise.
The Trümmelbach Falls are part of the Lauterbrunnen Valley's 72 waterfalls
inside the mountain atTtrummelbach Falls – no link
A discussion of the mechanics of turbulent water flow are beyond the scope of this paper, but a few images will give an idea of the power associated with the turbulent flow of flood waters.
From left to right: turbulent water flow during a flood; Semi-Regular Structures found inside Random Turbulent Flow; Turbulent flow modeling
From left to right: Turbulent flow is created as water passes by an object; Turbulent flow is created when water passes by an object; golden reflection
© Laura Fitzpatrick 2014