• Blakely Aaronson

Mountains Floating on a Sea of Stone

In New Jersey it has been a summer of unprecedented wetness. I've now lived here for four years, and have never seen so many thunderstorms and power outages. It's been a chaotic past few weeks, with power out as many days as it is on, and even our running water shutting off at one point! The weather data for Chiapas in Costa Rica shows that they've been having a fairly sunny and mild July and August. If only we were there! The field work that Anirudh and I will do with Professor Oscar Lücke next summer is going to require us to be outdoors a great deal; I can only hope that the weather then will be accommodating. In the past, research I've done has looked similar to what we're doing now: manipulating available data using software. In CR, we'll be collecting our own data, and that means setting up and operating on the equipment that does the collecting. For the time being, Ani and I are focusing our efforts on learning theory. If tectonic plates shift and bump into each other, they must be sliding atop something that's not too rigid. The Lithosphere (the stony crust layer of the Earth we see) lies above the Asthenosphere (a plastic layer of below). Because this lower layer isn't quite solid, it can be deformed by the shape of the crust. Wherever there's a mountain, we're only seeing part of it, and that there's a greater part of it floating below on the gooey Asthenosphere. If that sounds like an iceberg, you're right! Both these ideas function on the theory of Isostacy. The great proportion of mass in those roots should be detectable when we search for the local gravitational field, but that doesn't always turn out to be the case... Quite a few scientists have tried to explain this. Mount Everest is named after one of them. Our best guess is that the crust must - while abiding by this iceberg principle - also have a sort of general overall equilibrium. If there's a mountain with a great volume of roots below it, and plains all around the mountain with little below them, how is it all balanced out? The higher volume roots of the mountain must have lower density. In a way, these large, low-density roots 'buoy up' the mountain, allowing it to float above the plains. Oscar and Dr. Levin taught Ani and I how to apply these kinds of corrections to our data. The image for this blog post comes from Oscar's paper (which you can find here); it shows two tectonic plates meeting, and one getting pushed below the other. We practiced modelling the gravitational anomalies that showed up around the tiny little white mountain in that figure. This coming week, our whole cohort will be meeting to discuss the next steps for the Fall. I think our little group will continue to explore the software we have, learn theory, and try to make good use of the data provided for us by previous groups.

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