 Our next speaker will be Daniel Kim, who will be talking about understanding the conversion of rock to regolith using numerical modeling in the critical zone of the Bukio Mountains, Puerto Rico. And go whenever you're ready, Daniel. Hey, can you hear me? Yup, perfect. Oh yeah, thank you very much for the introduction. Hello, I'm Daniel Kim. I'm the postdoc at Tulane University. I'm working with Nicole Gasperini, Reynolds Cowell, Jane Williambrink, and Emma Harrison. Today, I'd like to talk about the size distribution model affected by weathering using numerical model. This project is funded by the NSF. The grain size distribution depends on weathering process to understand the relationship between weathering and grain size is important because grain size can affect the shape of a hill slope as well as channel bed. Scholar's 2017 research presented our model for the transformation of an initial grain size distribution. So my research simulates this model by using numerical modeling tool. Before we dig into a specific model, I would like to introduce my study area briefly. The solitude of my study area is almost unique. Uniform, most of the study area consists of cork-style light and minor area consists of volcanic rock. The study area shows a transient landscape. The erosion rate on the upper portion is 50 millimeter per kilowatt from cosmopolitan red-unicorn light. However, the low-up portion solution is two times larger than one on the upper part. The channel profile and histogram of elevation results also indicate the transient landscape. We can see separated area clearly around 600 meters. So some research told the adjusting area is propagating to the upstream. Yes, we can see silt clay size grain on the valley area. Meanwhile, we can see sand and granular size grain on the adjusting area. The study area experienced a tropical climate. The range of a mean annual rainfall is around one to five million per year. And the mean annual temperature is 22 to 28 degrees Celsius. So they found the regression equation with elevation. So we use this regression equation. Now I'm going to talk about the theoretical information we used. Upper equation is about the relationship between grain size and weathering. Barum equation is weathering function, W. It includes the solgene, climate and erosion properties. At this time, I focus on the impact of erosion properties. The right figure tells the relationship between weathering and erosion rate. Simply saying, higher erosion rate causes less weathering and less residence. In addition to that, we consider two erosion thresholds. ESK is an abbreviation about the transition between supported limited and kinematically limited. If the erosion rate is larger than ESK, the grains start to move. EKU is an abbreviation about the change between kinematically limited and no residence. When the erosion rate is larger than EKU, the grain doesn't get any weathering process and residence, which means it is still fresh. So I simulated the models following this process. Scholars study tested many scenarios, such as different initial grain size, bimodal input grain size distribution, et cetera. However, in today's presentation, I considered one case of grain size input and we changed the erosion properties. Result one showed the impact of erosion rate. To test it, I made initial grain size distribution on the whole catchment and got the result like this. To test the impact of erosion rate, the erosion rate below the point increased five times. The result tell pipe size is closer around an order of magnitude. This slide, we check the impact to erosion threshold EKU and ESK. Case one, the erosion rate of two areas are larger than EKU, which means no weathering process. Grain size, size is not changing. Case two, grains of the lower area is not weathered, but grains of the upper area is finer than case one. Case three, grains of the upper area get intense weathering, but grains of another area get less weather than case two. Case four, grain of two area experience intense weathering. So we get the finest grain size, but it's really exciting is that erosion threshold changes size distribution, even though erosion rate is not changing. We set the threshold slope to test the impact of Alkra. We define the area over 35 degrees as an Alkra. The results show three mode, but unfortunately the frequency of Alkra is too low because there is less steep area over 35 degrees. It consists of only five percent. However, it can see a dynamic result when you change the setting. In summary, our preliminary study indicates the grain size distribution depends on not only erosion rate, but also erosion rate threshold and steep area. But this model needs something to become a better model. First, this model considers unimodal input only. So I will test bymodal initial grain input and different input size. Second, this model needs a sensitive checkup to find more specific parameter space. Third, this model focuses on the hills of the process only. It needs to couple with the channel process. Finally, I will make this model into the component of land land. Thank you very much for listening to my presentation. Hey, thank you, Daniel. Well, if anyone has questions, please add them to the chat or raise your hand. So while we wait, I was curious about that climate term in the, when you were talking about weathering as a function of pathology, climate and erosion. I was just curious what was in the climate term. This equation is from scholars 2017 paper. So it is relationship between precipitation and temperature. Okay, it looks like people are still thinking of questions. So I'll encourage people to write questions in the chat. Okay. But for, oh, Greg is asking, I realize you're focused on the hill slopes, but are there any data that indicate how rapidly classed in the Lupea attenuate as they move downstream? I'm sorry, the ceiling was made. I cannot hear you. Sorry, look at the chat. Oh, okay, okay. Oh, yeah. So actually we are just going to go on a field trip last March to check up the, you know, Greg mentioned, but, you know, yeah. But unfortunately we did not check it because of pandemic. So yeah, actually this is a preliminary result. So it's gonna improve the model to make it more realistic.