One flood. Three days -> One canyon.

We often get glimpses into the overwhelming power of nature. One such was in June-July 2002 in Texas: Fearing the worst during torrential rains, the waters of Canyon Lake (a reservoir on the Guadalupe River) were diverted into an emergency spillway. The consequential flood event, with a flow rate of over 1450 cubic metres per second and duration of six weeks, destroyed a bridge and trees, and carved a 2.2 km long, 7 m (average) deep canyon into the limestone bedrock. This new Canyon Lake Gorge is highlighted by Michael Lamb (Caltech) and Mark Fonstad (Texas State University) in their paper published in Nature Geosciences on the ‘Rapid formation of a modern bedrock canyon by a single flood event’.

Deep river canyons are considered to have formed gradually over the millions of years as a result of moderate and recurring flow of water. Megaflood events too results in similar canyons and channels, except that these are formed more rapidly, as in the case of the Canyon Lake Gorge. In this event, it is undeniably known that the erosion happened during the flood and the more destructive episode happened over a time span of just three days.

Using pre and post data and techniques (aerial photographs/images, models, flood measurements) Lamb and Fonstad analysed the formation of the canyon, identified the characteristics, and reconstructed the hydraulics of the flood. The important findings are:

- The rate of gorge erosion/formation was rapid, limited only by the amount of sediments carried by the floods. About 460,000 cubic metres of materials were dislodged, almost half of which were rocks. Even boulders with a size of 1m were plucked and moved downstream.

- The very creation of the canyon was dependent on the nature/characteristics of the bedrock. For instance, the aforementioned plucking of the 1m limestone boulders was facilitated by the fractures (horizontal bedding planes and vertical cracks probably due to tectonic movements) which were already present in the layered limestone bedrock.

- The rock type determined the resultant morphology of the canyon. The first part features 10-12m high waterfalls, channels, and terraces due to the plucking of the boulders. The latter part features sediment islands which are considered to be characteristic of large flood events.

Caveat: Is this a really megaflood (floods with a flow of1 million cubic metres per second) per se?

References:
Lamb, M., & Fonstad, M. (2010). Rapid formation of a modern bedrock canyon by a single flood event Nature Geoscience, 3 (7), 477-481 DOI: 10.1038/ngeo894

http://media.caltech.edu/press_releases/13357

South West Monsoons

Although the IMD states that the South West (SW) Monsoons are on the romp in the Indian subcontinent, I must admit that Trivandrum seems to be neglected so far apart from some insubstantial drizzles- a far cry from those old days when the school reopening (usually on June 2nd) coincided with deluges (the normal onset of SW Monsoons being 1st June) and one would have to suffer through the lengthy classes with soaked socks!

Even though the SW monsoons first hits the south peninsular region of India (comprising of the states/territories of Andaman and Nicobar Islands, Andhra Pradesh, Karnataka, Kerala, Lakshadweep¸ Pondicherry, and Tamil Nadu) before proceeding on to the north, the Northeast Indian states (Arunachal Pradesh, Assam, Meghalaya, Nagaland, Manipur, Mizoram, Tripura, Sikkim,West Bengal, Jharkhand, and Bihar) receives the most amount of rainfall (1098.1 mm in 2009), followed by the Central Indian states (Gujarat, Madhya Pradesh, Maharashtra, Goa, Chhattisgarh, and Orissa) with 795.5 mm. The historical data for the past decade also shows that the South Peninsular region experiences the monsoons’ fickleness (682.3 in 2009; 692.5 in 2008; 902.1 in 2007; 684.5 in 2006; 807 in 2005; 617 in 2004; 648 in 2003; 506.7 in 2002; 659 in 2001; 801.3 in 2000), with the region receiving less than 700 mm in 1999, 1993, 1987-1984; 1982; 1979; 1980; 1977-76; 1973-71. The region’s normal rainfall in June averages 200-300 mm. And with Kerala receiving only 98.4 mm during the week of 27th May to 2nd June (a deficiency of -57%), I am fervently hoping that there won’t be another drought.

*All data and units are from IMD

Addendum: Mercuric

I mentioned in ‘Mercuric’ of how traditional eco-friendly Keralite house (similar to a Roman villa) featured nadu muttams, like the Peristylium, and often an Impluvium to collect rainwater. Unfortunately, nadu muttams also tends to ease the burglars’ game plans. As a result, house owners have now come up with various solutions, including installing a grille along the corridors, or affixing fibreglass above the muttam. Those who installed wire meshes found their efforts to be futile. Another option was followed by the current residents of my mother’s maternal home, which used to have three nadu muttams: these have now been converted into rooms.
Any ideas of how to maintain a burglar-safe nadu muttam?

Since my previous post, after the appearance of rainclouds in the evening, we are expecting some respite, although a local climate expert has dampened these hopes by stating that the resultant showers, if any, will be light. The more aged astutes are predicting torrential cloudbursts. The seas are apparently exceptionally rough.