Morphodiversity of the Mixteca Alta UNESCO Global (Oaxaca, Mexico)

The Earth's surface is not a uniform canvas; it is a complex tapestry woven from rock, soil, and water, each layer telling a different story of how the landscape was formed. Scientists who study this variety, known as geodiversity, often rely on detailed maps of geology and soil to understand a region's character. These maps are essential for protecting natural heritage and planning how people interact with the land, such as in UNESCO Global Geoparks, which are areas recognized for their significant geological features. However, in many parts of the world, these detailed maps simply do not exist at the scale needed for modern management. When the traditional paper maps are missing or too vague, researchers must find another way to measure the richness of the terrain. They have turned to digital models of the ground, which act like precise, three-dimensional photographs of the Earth's surface, allowing them to calculate the shape and texture of the land directly from the data itself.

In the Mixteca Alta region of Oaxaca, Mexico, a UNESCO Global Geopark known for its rugged mountains and deep valleys, researchers faced exactly this challenge. The area is geologically complex, containing ancient limestones, volcanic rocks, and river deposits, but the available maps were not detailed enough to guide conservation efforts or tourism planning effectively. To solve this, a team of scientists used a high-resolution digital model of the terrain to measure three specific qualities of the landscape: how steep the ground is, the shape of the slopes, and the roughness of the surface. By breaking these qualities down into classes and combining them, they created a new map that reveals the "morphodiversity" of the region. This approach allowed them to see the landscape's variety without needing the missing geological maps, providing a clear picture of which areas are complex and sensitive and which are flat and uniform.

The researchers focused on three main attributes to build their picture of the land. First, they measured the slope, or the angle of the ground, dividing it into categories ranging from flat to extremely steep. They found that more than half of the geopark consists of mountainous terrain with slopes steeper than nine degrees. Second, they analyzed the shape of the slopes, looking for concave areas like riverbeds, convex areas like mountain ridges, and flat surfaces. This helped them distinguish between valleys and the high points that separate them. Third, they calculated the roughness of the surface, which describes how jagged or irregular the ground feels at a small scale. This measurement is based on how much the surface fills a three-dimensional space; a smooth plain has low roughness, while a jagged, rocky surface has high roughness. By combining these three measurements, the team could assign a diversity score to every part of the park.

The results revealed a landscape divided into distinct zones of complexity. The southern part of the geopark, covered by river deposits, showed very low morphodiversity. These are the flat, gentle plains where the ground changes very little, making them homogeneous and easy to traverse. In contrast, the mountainous areas, particularly those formed by volcanic rocks like tuffs and andesites, displayed very high morphodiversity. These zones are characterized by steep slopes, sharp ridges, and rough, uneven surfaces. The limestone hills and intermontane valleys fell somewhere in the middle, showing an intermediate level of variety. The study also tested how the size of the area being measured affected the results. They found that while the specific numbers changed depending on the scale, the overall pattern remained consistent, confirming that the method is robust enough to identify the major features of the terrain reliably.

A key discovery was that the shape of the slopes played a unique role in defining the landscape's character. When the researchers gave more weight to the slope shape in their calculations, the resulting map showed much more variation and detail than when they focused only on steepness or roughness. This suggests that the way the land curves—whether it dips into a valley or arches over a ridge—is a critical factor in understanding the area's diversity. The study also compared their new method against traditional geological maps. They found that the old maps, which only showed broad boundaries between rock types, failed to capture the fine-scale diversity that the digital model revealed. In areas where the rock types are mixed or the terrain is complex, the traditional maps appeared too simple to be useful for detailed planning.

The implications of these findings are practical for managing the geopark. The areas with high and very high morphodiversity, where the terrain is steep and rough, are identified as priority zones for conservation. These are the places where the natural heritage is most complex and where visitors can see the most dramatic geological features. Conversely, the flat, low-diversity areas in the south are better suited for infrastructure, such as visitor centers or roads, because they are less sensitive to human impact. By using this digital approach, park managers can make informed decisions about where to build facilities and where to protect the land, ensuring that development does not damage the most fragile and interesting parts of the landscape.

This work demonstrates that even without detailed geological maps, it is possible to understand and manage a region's natural heritage using digital tools. The method provides an objective way to measure the variety of the land, turning raw data into a clear guide for conservation. It shows that the Mixteca Alta is a place of striking contrasts, from the smooth, quiet plains to the rugged, volcanic peaks, and that understanding these differences is the first step toward preserving them. By focusing on the actual shape and texture of the ground, the researchers have provided a tool that can be used to protect the unique character of this UNESCO Global Geopark for future generations.