Visualizing 3.7 million tons of sediment
For one of my Ph.D projects I’ve been investigating the flux of terrigenous sediment into a deep marine basin over the last 7,000 years. I ended up calculating the volume of sediment that has accumulated over this time using high-resolution seismic-reflection data that is tied to radiocarbon-dated cores.
The variability and controls of sediment flux to the basin is an interesting story that I will save for a future post (I want to get the paper submitted first). For this post, I will talk about some absolute numbers that came out of the analysis that are kind of interesting as factoids. The average sediment accumulation in the basin over the 7 kyr when converted to mass is 3.7 million tons of sediment per year. This made me wonder…how much sediment is that?
The standard ‘gondola’ style freight train boxcar…the kind that are open on the top and carry gravel, coal, steel, and similar cargo…is 16 m long and has a 77 ton capacity (give or take). A train that carried all 3.7 million tons of sediment would have over 48,000 cars and be nearly 770 km long. This train would stretch from San Francisco to San Diego (or New York City to Cleveland; or London to Dundee, Scotland, etc.).
So, that was the amount of sediment delivered per year…what about the total for the 7,000 years. The total accumulated sediment is 26 billion tons. This cargo train would have over 337 million cars and be 5.4 million km long stretching around the Earth 135 times. That’s a lot of sediment.
As an aside, a 2003 study by Syvitski et al. calculated the total sediment flux from rivers to the ocean for the entire globe at ~20 billion tons/year. A nice number to keep in your back pocket and pull out at cocktail parties.
Syvitski, Peckham, Hilberman, and Mulder, 2003, Predicting the terrestrial flux of sediment to the global ocean: A planetary perspective: Sedimentary Geology, v. 162, p. 5-24.