Early Career Spotlight

Nakul Deshpande

Tell us about yourself:

Hi! My name is Nakul Deshpande - I was born in Philadelphia on the eve of the season 2 premiere of David Lynch's Twin Peaks and the official start of USGS water year `90 -`91. My childhood featured a lot of legos, trains and chess games nestled in Chamisal, a village (or, officially: a census-designated place) in the mountains of northern New Mexico. I thought about/worked on rocks and waterfalls at UC Santa Cruz as an undergraduate, hustled a giant logjam at Idaho State University during an MS., and have returned to the city of my birth where I am a PhD candidate at the University of Pennsylvania.

What is your research about?

The premise of my PhD work is admittedly naive at a first glance: what happens when a pile of sand is poured on a table and left to just sit there - and what can this can tell us about soil-mantled hillslopes? Our intuition is that the sandpile is immobile, frozen, jammed -- no motion is to be found below the angle of repose. Indeed, this is the case if we look only with our naked eye. But when illuminated with laser light and clever optics - Diffusive Wave Spectroscopy (DWS) helps us render a different picture; one where we are able to measure grain motions on the order of the optical wavelength (10-6 m). This picture is one where quasi-random hot spots of tiny deformations traverse the sandpile -- and are observed up to 11 days after pouring (that's a million seconds, for those of you counting). Piles of kaolinite, playground sand, and mixtures of the two likewise creep: the phenomenology is robust across material types. When subjected to a pulse of heat, creep rates increase and the hotspots remain spatially heterogeneous -- similar to the picture when the grains are first poured. Thus, applied heat - a way to approximate the effects of freeze thaw or diurnal temperature fluctuations - `rejuvenates' creep in the sandpile. Gentle taps induce a different response: creep rates slow and the spatial response is confined to a localized, thin surface layer -- tapping induces `aging'. When compared with decades (!!) of field observations compiled from `Young Pits' (passive tracer pegs buried for years and then excavated), sandpile creep is quantitatively consistent, demonstrating that much of the essence of a natural, `real life' creeping hillslope is captured in an idealized physical experiment. Simply put: hillslopes in experiments and the field persistently creep and are perpetually fragile - susceptible to minute perturbations and unable to attain a fully stable state. This view of hillslope soil creep is fundamentally distinct from the `diffusive' paradigm to which we look for slope-flux formulations to model landscape evolution. I am now looking to frameworks in soft matter physics to contextualize hillslope creep phenomenology within the realm of glassy materials and other disordered, amorphous solids.

What excites you about your research?

I find most things around me a mystery. `Research' is another name for what I see as an attempt to poke at this mystery and get closer to its center. For me, it is a curiosity-fueled work that seeks to builds on rigorous, modern frameworks and styles of thinking where the joy is in the work itself. Because there are other folks (some of them scientists) who also somehow feel the same - I am lucky to learn from and with them. This makes the process of research worthwhile and exciting. Geomorphology (and the geosciences in general) is an excellent playground for this process and these collaborations; the Earth system features such an array of weird, cool stuff and all of us live here -- so the opportunities are ripe!

What broader importance does your research have for society?

I find it difficult to answer this question. We are in the midst of a global crisis in which certain branches of science are critically important for society. Lives depend on it. I don't know that soil creeping on a hillslope or my sandpile sitting in the basement lab has importance to society at this moment; I am hesitant to claim that it has any concrete importance at all. Nevertheless, within my work, there are kernels of relevance to society. First, the light scattering technique I use to measure creep has been used to measure the lifetime of fluid droplets suspended in air; with consequences for the transmission of SARS-CoV-2. Clearly, the power of light scattering is to render that which is slow and normally invisible in a new light. This is important in opening our eyes beyond what our senses readily and easily provide to us. Secondly, hillslope soil creep is not just about things moving slowly; what looms in the background is creep as the harbinger of catastrophic failure as hillsides accelerate to generate landslides and debris flows. These hazards are devastating to communities and infrastructure. Linking creep to failure is important in hazard mitigation and in the most idealized scenario - forecasting failure itself. Third, creep is not unique to hillslope soil or granular materials -- it is ubiquitous in disordered, amorphous solids; namely glasses. Glasses abound in our daily lives - from household objects and materials to infrastructure and the built environment. By embracing soil (and indeed, the whole of Earth's surface) as a kind of dirty, noisy glass, we deepen our understanding of the underlying and ubiquitous materiality of the world in which we are embedded.

What inspired you to pursue a career in Earth science?

Beauty is everywhere in the Earth system. Beauty is inspiring. Many of us trace the inspiration to learn about landscapes to our childhoods, where we spent lots of time playing outside. I think that this is telling; that there is something in conducting science that allows us to reach back in time to our experience as children. I think that this spirit is very important. As a kid I spent a healthy amount of time trundling in the acequia, staring at pebbles, bugs, and the shape of flowing water. I also was moved by films (westerns and Tarkovsky) featuring magnificent landscapes whose plots are woven from the landscape itself. In essence, I like learning and I feel an affinity to landscapes and nature, so I welcome work that is fun, gives me the opportunity to learn, and is connected to the land.

What are you looking to do after you complete your PhD or postdoc?

Many things are possible! As an example, - an academic life of research and teaching is one answer to this question, and would look something like this: I seek a space that values Earth Science and physics (soft matter, disordered systems and statistical physics), where I can be free and conduct independent science. Through this science, I would practice a style of geomorphology that looks to other fields to borrow techniques and frameworks and enrich our view of the Earth's surface. I would like to be surrounded by scientists who are as kind and open-minded as they are brilliant and accomplished. This place would value teaching undergraduates and support graduate students. Much is lost without teaching and the transmission of experience between one generation and the next. I would like to believe that this place exists and that I would be useful to the community within it.

Given unlimited funding and access to resources, what is your dream project that you would pursue?

Dreams! I have many of these -- and I can see many ways to build projects that link soft-matter physics and geomorphology: volcanoes, eco/bio/geo couplings, glacier-sediment systems, tectonic-scale dynamics... so many possibilities... what they all require are toys, toys galore! First, science isn't done without well-fed and cared after humans -- I would first hire a team of folks who are smarter than me, who have skills I don't, who would want to work with me and who I want to learn from. I would hire students and pay them well. Our rooms and labs would have windows and there will be snacks. I'll indulge in some of the science toys/tools I would buy to fill a lab space for any one of these projects. Much of my PhD work consists of experiments conducted on vibration-isolated optical tables - a few of these for good measure - a handful of lasers and a bucket of cameras and optics. Bins of grains. Throw in a workbench with some powertools and a corner for soldering and electronics work. Comfy chairs. A few chalkboards. This is my dream project - the space and community to do whatever cool, whacky science I fancy.

What else do you do?  Any hobbies or interests outside of work?

I am a musician - whenever I have the opportunity, I spend time with musician friends and study at the Labyrinth Musical Workshop in Crete. I play the lyra -- a kind of `knee fiddle' which has numerous incarnations - the Bulgarian gadulka, Turkish kemençe and south Asian sarangi are all examples of lyra-family instruments. My lyra is one with sympathetic strings and is made by Stelios Petrakis -- a true experimentalist. Folk and art musics of the pan-Mediterranean can be played on the lyra - and creative new forms which fold in the old influences are especially beautiful to me. I also like chess! I am currently on study 347 of 2,545 in Kasparyan's endgame book. Next time you catch me - please ask me more! I am happy to share about music, chess, or my other favorite hobby, science.


Nakul standing on a logjam in Big Creek, Idaho