As winds blow from east to west across the Sahara, they pick up great quantities of clay, silt, and sand. Let’s call these particles “dust.” The strongest winds then carry the dust across the Atlantic to the Lesser Antilles and to South America. The ocean floor has detectable amounts of Saharan dust, and the tropical rainforests grow in soils revitalized by the dust.
Sedimentologists recognize sediment by both its composition and by the size of its individual particles, called clasts. Boulders are the biggest clasts. Cobbles are smaller. There are pebbles, of course, and three sizes of sands: coarse, medium, and fine. Smaller yet are the silts, and even smaller are clays. The smallest are colloidal particles.
These clasts move by gravity and fluid flow, such as the fluid movement of air and water. They move until there’s no more energy to move them, and then they settle out of the fluid, they drop; they become sediments. As you read above, Saharan winds can carry sediments thousands of miles. Streams like the Mississippi, the Nile, and the Amazon also carry sediments great distances. As long as the flowing medium has sufficient energy, the sediments move. As energy ebbs, sediments drop.
The biggest clasts are very difficult to move because of their mass. They require a great deal of energy. Smaller clasts are generally easier to move. You can’t blow on a boulder to move it, but you can move small pebbles with your breath, and sands and silts are easy to blow off your picnic table at the beach.
Like the winds of the Sahara, you also spread your influence, making an impact sometimes so far that it occurs over the horizon. Typically, the distant influence you effect is rather small, generated by the tiniest of your scattered thoughts and behaviors. Big influences are usually more local. If you want to move the boulders of your influence farther from their source, you have to be more energetic. Breezes do nothing to a boulder.
Sedimentologists recognize sediment by both its composition and by the size of its individual particles, called clasts. Boulders are the biggest clasts. Cobbles are smaller. There are pebbles, of course, and three sizes of sands: coarse, medium, and fine. Smaller yet are the silts, and even smaller are clays. The smallest are colloidal particles.
These clasts move by gravity and fluid flow, such as the fluid movement of air and water. They move until there’s no more energy to move them, and then they settle out of the fluid, they drop; they become sediments. As you read above, Saharan winds can carry sediments thousands of miles. Streams like the Mississippi, the Nile, and the Amazon also carry sediments great distances. As long as the flowing medium has sufficient energy, the sediments move. As energy ebbs, sediments drop.
The biggest clasts are very difficult to move because of their mass. They require a great deal of energy. Smaller clasts are generally easier to move. You can’t blow on a boulder to move it, but you can move small pebbles with your breath, and sands and silts are easy to blow off your picnic table at the beach.
Like the winds of the Sahara, you also spread your influence, making an impact sometimes so far that it occurs over the horizon. Typically, the distant influence you effect is rather small, generated by the tiniest of your scattered thoughts and behaviors. Big influences are usually more local. If you want to move the boulders of your influence farther from their source, you have to be more energetic. Breezes do nothing to a boulder.
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