by Philip S. Prince Landslides can be triggered by a variety of conditions or events. Erosional removal of the base, or toe, of a steep slope is a common cause of landsliding, sometimes creating “stop and go” landslides that move episodically when erosion carries away just enough material to create instability. After a bit of slide movement restores the shape of the slope toe, movement stops until…
by Philip S. Prince Pleistocene-aged sand dunes are some of the most conspicuous lidar features of the southeastern United States Coastal Plain, largely because their lumpy surfaces and non-erosional outlines contrast sharply with other “background” landforms. It’s hard to imagine the modern-day swampy Coastal Plain being much less forested and windy enough to be covered with migrating sand dunes,…
by Philip S. Prince While Earth’s most dramatic geologic fold structures result from compressional deformation, extensional deformation can also produce closed, upright folds–in both the real world and in physical models. Extensional anticlines (particularly when upright and generally unfaulted) are always more subtle than their compressional cousins, but extensional synclines can be very tight…
By Philip S. Prince If you have studied geology in recent decades, you have probably encountered a cross-cutting relationships exercise, particularly in a lab class. These exercises are an important part of establishing the order in which particular events occurred, and thus understanding which structural and stratigraphic feature may impact–or be impacted by–other features. Most cross-cutting…
by Philip S. Prince Landslides occur regularly along the rugged Blue Ridge Escarpment in western North Carolina, and lidar imagery provides a way to easily view the accumulated scars of these events that are preserved in the landscape. With a high quality (0.5-meter resolution) lidar dataset, it’s hard to examine much of the Escarpment without seeing a few landslide features. Some slopes have more…
by Philip S. Prince If you spend any time on the internet, you’ve probably seen an image of China’s Zhangye Danxia Landform, also known as the “Rainbow Mountains.” While these colorful landforms get most of the hype, China hosts another, arguably more impressive, zone of colorful, tilted sedimentary layer mountains–the Keping fold-and-thrust belt. Located at the northern edge of the Tarim Basin,…
by Philip S. Prince The January 20, 2023, landslide at Blacks Beach near La Jolla, California, dramatically uplifted a small portion of the beach during the slide’s movement. Filmmaker Kent Ameneyro captured the uplift sequence in great detail in the YouTube video linked here. From ground level, the uplift is very dramatic, particularly against the backdrop of the downward displacement of the…
by Philip S. Prince Reproducing fold structures observed in sedimentary rocks has kept geologists busy since the 19th century. Early model faults and associated folds (H. Caddell and B. Willis, for example) were produced by compressional deformation of a variety of layered materials, and an intuitive association certainly exists between buckle folding and squeezing/shortening a sequence of layers.…
by Philip S. Prince The speed and mobility of debris flows make them particularly dangerous among landslides. Debris flows move so quickly because they are fluidized masses of saturated soil, boulders and rock fragments, wood, and water, which causes them to erode or scour their flow path and accumulate more material than initially failed on the slope. The eroded track left by the scouring process…
by Philip S. Prince Inversion of normal faults during compression is a popular topic in structural geology, but thrust or reverse faults can also be inverted by extension. Like inverting normal faults, favorable fault dips are an important part of this process, particularly when it is reproduced in a sandbox model like the one shown below. This model developed an initial steep thrust fault due to…