Beware the bubble’s burst
Increased knowledge about cavitation highlights the destructive power of fast-flowing water
Published: 24 October 2007(GMT+10)
This is the pre-publication version which was subsequently revised to appear in Creation 31(2):50–51.
Photo Erik Axdahl Wikimedia.org
Cavitation damage to a ship’s propeller
When Britain’s Royal Navy ships were suffering considerable and unexplained damage to their ships’ propellers in WWI, physicists worked out that violent ‘bubble cavitation’1 was the cause. This happens because tiny bubbles grow and then collapse as a result of pressure variations in the turbulent water around a propeller. But nobody knew just how hot the bubbles could get before releasing their destructive energy.
However, in recent years researchers have found that temperatures inside the tiny bubbles can rise so high that the bubbles start to glow. In fact, there’s evidence that temperatures can rise as high as 15,000 Kelvin (~15,000ºC; 27,000ºF). 2 This indicates that the collapsed bubble has a hot plasma core, i.e. ‘as hot as the surface of a bright star’.3
Little wonder then that fast-flowing water can cut through solid concrete in dam tunnels—as happened at Glen Canyon Dam in 1983.4 Unexpected flood rains put such pressure on the dam’s tunnel spillways that after a few days a ‘slight rumbling and vibration’ began to be felt in the abutments and the dam itself. At that time, observers of the jets of water emerging from the tunnel portals noticed debris being forcibly ejected in the flow of water. The debris included ‘chunks of concrete, sections of rebar, and most disturbingly, what looked like pieces of sandstone, arced high above the river’.4
With no letup in the rain, Glen Canyon Dam levels rose further, and the discharge from one of the spillway tunnels ‘was turning the whole river below the dam [into] a distinct amber color.’ As one analysis of the event put it: ‘Navajo sandstone was being excavated from within the dam abutment like soil before a placer miner’s hydraulic nozzle.’4
it sounded like the artillery barrages he had experienced in Vietnam
Down in the employee dining room, located near the hydroelectric power plant at the base of the dam adjacent to the left abutment, a worker later said that it sounded like the artillery barrages he had experienced in Vietnam.
Photo Bureau of Reclamation, U.S. Dept of the Interior
Glen Canyon Dam tunnel spillway damage in 1983
Afterwards, inspection of the worst-affected tunnel revealed a hole carved through the reinforced concrete into the sandstone. It was almost 15 metres (50 ft) deep and 45 metres (135 ft) long. A giant boulder (3 metres x 4.5 metres, or 10 ft x 15 ft) was found half-way down the tunnel (i.e. beyond the hole). The other tunnel had less severe damage, but, ‘One-inch [25-mm] rebar had been pulled out of the concrete like bones from a cooked fish.’4
The US Department of Interior later reported that it was cavitation that had started the damage, followed by dramatically increasing mechanical erosion. Interestingly, in our 1997 interview with cavitation expert Dr Edmund Holroyd, who is also a creationist, he told us of his strong belief that ‘cavitation is very important in helping us understand how massive erosion would have taken place in the early stages of the [Genesis] Flood’. Dr Holroyd was only too familiar with the potential5 destructiveness of cavitating water:
‘When water less than 10 metres deep is flowing at very high speed (say 30 metres a second) and goes over a bump, it can turn into water vapor via the formation of tiny bubbles. These collapse again when the pressure is restored, and they do so at a supersonic speed which creates shock waves with incredible pressures. This pulverizes the surface right next to where the bubbles are collapsing, so it can “eat” rock surfaces away much, much more quickly than normal erosion. In the laboratory, such cavitating water will even rapidly “eat” a steel surface.’6
Given the destructive power of rushing water, can you imagine the legacy of the global Flood? As we look around the earth’s landscape today, it’s easy to find leftover ‘signs’ of the cataclysmic inundation described in Genesis 6–9. The world is full of steep-sided gorges, canyons and ravines, eroded by the enormous floodwaters as they receded off the continents! As our knowledge of this phenomenon of cavitation grows, it surely helps us understand a little more of the massive erosion forces at work during the Flood—unless, of course, one is too ‘blind’ to see:
First of all, you must understand that in the last days scoffers will come, scoffing and following their own evil desires. … But they deliberately forget that long ago by God’s word the heavens existed and the earth was formed out of water and by water. By these waters also the world of that time was deluged and destroyed.
- Cavitation is somewhat like boiling. Even non-boiling liquids have some molecules escaping as gas, and some of these molecules return to the liquid. At equilibrium, the gas has a certain vapour pressure. Boiling occurs when the liquid is hot enough to raise its vapour pressure above atmospheric pressure. At high altitude, it takes a lower temperature to boil because the atmospheric pressure. Cavitation takes this a step further: the fast flow of a liquid lowers the pressure by the Bernoulli effect, and when the pressure drops below the vapour pressure, bubbles of vapour are produced. Shallow water is worse because there is less pressure from the weight of the liquid. The damage is caused when the bubble bursts, since the pressure of the surrounding liquid is very high for small bubbles (inversely proportional to the radius). Return to Text.
- Flannigan, D.J., and Suslick, K.S., Plasma formation and temperature measurement during single-bubble cavitation, Nature 434(7029):52–55, 3 March 2005. Return to Text.
- Lohse, D., Cavitation hots up, Nature 434(7029):33–34, 3 March 2005. Return to Text.
- Hannon, S.,
The 1983 Flood at Glen Canyon, Glen Canyon Institute, <http://www.glencanyon.org/publications/hiddenpassage/
hp2stev.php>, acc. 17 October 2007. Return to Text.
- We do not see cavitation in every situation with fast-flowing water because conditions are not always conducive for it to occur. For example, as Dr Holroyd points out, water flowing over topographical ‘bumps’ and ‘holes’ is more likely to cavitate than water flowing over a smooth surface. Very high rates of flow are required—shallow water (< 10 metres deep) must be flowing at speeds of at least 30 m/s—and the deeper the water, the greater the speed required for cavitation. Holroyd, E., Cavitation processes during catastrophic floods, Proceedings of the 2nd International Conference on Creationism July–August 1990, pp. 101–113 (note especially pp. 108–109). Return to Text.
- Cardno, S., and Wieland, C., Clouds, coins and creation: An airport encounter with professional scientist and creationist Dr Edmond Holroyd, Creation 20(1):22–23, 1997. Return to Text.