This map shows sea-surface temperatures averaged over eight days in September 2001, as measured by NASA’s Terra satellite. Dark red represents warm water (32°C) and purple is cold (–2°C). The Gulf Stream can be seen as the orange strip extending from the eastern U.S. PICTURE CREDITS toward the Atlantic. 2 — Ronald Vogel, SAIC for NASA GSFC; 3 — Genping “Roots” Liu; 4, 10 — Lance Hayashida; 5 — Charles Decker; 7 — Katie Neith; 9, 11 — Jenny Somerville

Wall of Sound ’MID THESE DANCING ROCKS

Over 50 members of the Caltech The following real-world paradox A huge flume recently installed on Jazz Bands and the Caltech-Occi- comes to you courtesy of Assistant the Caltech campus just might provide dental Concert Band brought the Professor of Geology Michael Lamb: some answers. A flume is an artificial sound of music to the Great Wall “Say you’re out hiking, and you come river—in this case, a tilted rectangular of China in March. Positioned in front to a roaring stream plunging down chute down which water cascades. of a fort on a portion of the wall near the side of a mountain. It’s full of Explains Lamb, “We can load our Beijing, the group played a concert rocks and boulders, all precariously flume with various sediments, includ- featuring two new pieces written balanced. You come back the next ing fair-sized rocks, tilt it at any angle specifically for the occasion.O ne year, and you find that those same up to 15 degrees, and change the rate of the world premieres was written rocks are still there, just where they of flow of the water. That gives us a by Caltech alumnus Leslie Deutsch were. In fact, year after year you way to simulate all kinds of rivers.” (BS ’76, MS ’77, PhD ’80), chief come back, and they never seem Rocks, water, slope—surely there technologist for the Interplanetary to move. Why is this?” must be more to simulating a river than Network Directorate at JPL; the other Don’t know the answer? Neither that? “Surprisingly, that’s complicated was written by his son, Elliot, a jazz does Lamb, and he’s been thinking enough,” shrugs Lamb. “Water, on its bandleader, composer, and trumpeter. about it for a long time. Loose rocks own, we understand fairly well. We The featured vocal soloist, Kjerstin on the bottom of lazy, low-sloping riv- know the equations that describe Williams (BS ’00, MS ’02, PhD ’06), ers migrate slowly downstream under how it flows in a smooth channel. lent her voice to the jazz tunes. The nature’s inexorable nudging. But in But as soon as we start introducing group also joined fellow musicians very steep channels, where it would sediment, the coupling between from Tsinghua University for a joint seem that the collaboration between moving sediment, immobile sediment, concert in Beijing. —KN water and gravity should produce and water becomes quite a compli- much more dramatic results, much cated problem. We don’t even know of the stuff on the bottom stays put. the equations to describe it.” And no one knows why. The flume hulks in one corner of the Central Engineering Services building’s machine shop, filling virtually every cubic inch of available space. It features a main section more than 15 meters long and, bone-dry, it weighs

“Playing on and climbing the Great Wall was definitely a highlight of the trip. It will be something that I will be able to talk about for decades after I graduate from Caltech, since it will always stand out from the everyday life of a Techer,” said freshman clarinetist Hima Hassenruck-Gudipati.

spring/summer 2011 ENGINEERING & SCIENCE 3 15 tons—simply dwarfing most of the “Typical flume research,” Lamb weathering rates are tied to the high- other laboratory flumes in the world continues, “uses sand or even finer est erosion rates. In the Himalayas, capable of such steep slopes. Lamb sediments, which can be pumped for example, where rocks are uplifting didn’t design it this way from a bigger- right through the pipes along with rapidly and the rivers are eroding is-better mentality, but because he’s the water. But we’re looking at rapidly, weathering may be drawing

interested in complexities that can’t the much coarser objects found in enough CO2 out of the atmosphere be modeled on smaller scales. “Imagine mountain channels.” Rocks the size of to affect global climate. But if I stood a steep mountain stream where the softballs or soccer balls don’t normally in front of a mountain river with the boulders have organized themselves mix well with high-speed pumps, so a most knowledgeable people in the into steps,” he explains. “There’s a system of external conveyors collects world, and asked them to tell me how boulder that makes a little waterfall, the accumulation in the tailbox and fast that river was cutting, or how with a pool at the bottom, and below returns it back to the head. much sediment would come out of that there’s another boulder making Lamb’s plans range from study- it in a year, they wouldn’t be able to another waterfall with another pool, ing issues of local concern, such as tell me within a factor of ten. We just and so on. In order to understand how debris rumbles down a denuded don’t have the observations yet to how the sediment organizes itself mountainside after a wildfire, to the know how these systems work. into these structures, and how the global connection between ero- “A lot of research has been done structures then feed back into the sion and climate change. “When on low-sloping, big channels: how system, we’d need to create three you weather silicate rocks into clays, to engineer them, how to dam them, or four step-and-pool sequences in a you’re sucking carbon dioxide out of and so forth. That makes sense, row. You can’t do that in a small flume.” the atmosphere. But once the rock is because we live in a world full of A remotely controlled cart trundles covered by a layer of clay, the weath- cities built on rivers. But small, steep back and forth atop the length of the ering process shuts down unless you mountain channels play a critical role flume, bearing high-precision instru- physically transport that material away in shaping our terrain and climate ments that map both the surface and and expose fresh bedrock to more over long timescales, and we know the bottom of the artificial river with weathering. So the highest chemical very, very little about them.” —DZ submillimeter accuracy. Water over- flows into the flume’s upstream end from the headbox, which is constantly refilled at whatever rate is needed in order to simulate anything from a trickling creek to a roaring cascade. The headbox is replenished from the tailbox at the flume’s downstream end by a pair of pumps. “The larger one is the size of a Volkswagen,” Lamb points out. “It can move 8,000 gallons of water a minute.”

A look into the empty flume. The flume can be tilted as much as 15 degrees, allowing water and sediments— such as rocks, pebbles, and dirt—to flow down and simulate everything from a creek to a cascade.

4 ENGINEERING & SCIENCE spring/summer 2011