Due to their potentially long runout, debris flows are a major hazard and an important geomorphic process in mountainous environments. Understanding runout is therefore essential to minimize risk in the near‐term and interpret the pace and pattern of debris flow erosion and deposition over geomorphic timescales. Many debris flows occur in forested landscapes where they mobilize large volumes of large woody debris (LWD) in addition to sediment, but few studies have quantitatively documented the effects of LWD on runout. Here, we analyze recent and historic debris flows in southeast Alaska, a mountainous, forested system with minimal human alteration. Sixteen debris flows near Sitka triggered on August 18, 2015 or more recently had volumes of 80 to 25 000 m3 and limited mobility compared to a global compilation of similarly‐sized debris flows. Their deposits inundated 31% of the planimetric area, and their runout lengths were 48% of that predicted by the global dataset. Depositional slopes were 6°–26°, and mobility index, defined as the ratio of horizontal runout to vertical elevation change, ranged from 1.2 to 3, further indicating low mobility. In the broader southeast Alaskan region consisting of Chichagof and Baranof Islands, remote sensing‐based analysis of 1061 historic debris flows showed that mobility index decreased from 2.3–2.5 to 1.4–1.8 as average forest age increased from 0 to 416 years. We therefore interpret that the presence of LWD within a debris flow and standing trees, stumps, and logs in the deposition zone inhibit runout, primarily through granular phenomena such as jamming due to force chains. Calibration of debris flow runout models should therefore incorporate the ecologic as well as geologic setting, and feedbacks between debris flows and vegetation likely control the transport of sediment and organic material through steep, forested catchments over geomorphic time. © 2020 John Wiley & Sons, Ltd.

A new series of introductory physics experiments for teaching the kinematics and dynamics of falling bodies is presented. These learning activities are enabled by newly available position-tracking technology that allows for the direct acquisition of coordinate data from moving objects. Students are led through an iterative inquiry process that explores both free fall and drag-enhanced physical models, for different velocity regimes, emphasizing a comparative modeling approach to science. Learners discover how the experimental design, including the properties of the dropped objects, the dropping distance, and the uncertainty of the measuring device, impacts the ability to explore the validity of physical models with or without drag.

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Tracking the motion of an object in 2D as a demonstration in a physics classroom or as a laboratory activity is difficult to accomplish in real time with traditional equipment used by educators. A local positioning system (LPS), like the Pozyx Creator series LPS, has a potentially wide range of educational applications for introductory physics courses. In a previous article we reported using this product to track one-dimensional motion, pressure, rotation, and magnetic field data, but here we discuss how such systems can provide location information (to within approximately ±10 cm) in one, two, and potentially three dimensions both indoors and outdoors.

Recently available local positioning systems (LPS) have the potential to be used for interactive physics laboratory activities and classroom demonstrations. The Pozyx LPS combines multiple sensors with position data for any object that one of the devices is attached to. Devices referred to as “tags” (Fig. 1[a]) are mobile devices that can be tracked, and those referred to as “anchors” are stationary devices that are employed to calculate the tag’s position. At data rates of 30 Hz (2D and 3D tracking) to 200 Hz (1D tracking), the position is measured to an accuracy of about ±10 cm. We have found that this particular LPS works best for physics laboratory setups at distance scales of at least two meters and up to tens of meters.