MAPPING MOKST BUTTE LAVA FLOW IN CENTRAL OREGON USING LIDAR REFLECTION INTENSITY DATA AND FIELD OBSERVATIONS

Lidar (light radar) has revolutionized the acquisition of high resolution topographic data, and allows quantification and interpretation of volcanic terrains in remote and inaccessible areas. For this project, lidar data, field work, and lava bulk compositions are being used to map the chronology and surface features of the Mokst Butte lava flows in central Oregon. Lidar intensities were used to remotely classify a wide variety of surface morphologies (lava surface features, vegetation, tephra, rafted cone material) of the lava flow field in ArcGIS.

Mokst Butte is a Holocene scoria cone on the northwest flank of Newberry volcano, east of the High Cascades, in central Oregon. Mokst Butte initiated as a fissure-fed eruption, as part of a series of eruptions along the Northwest Rift Zone (~7000 years ago), and centralized into a single scoria cone vent that produced a lava flow field to the south and northwest, covering a total area of 24 km².

Field observations and samples gathered during the summer of 2014 and by prior workers were used to compose a map of the Mokst Butte lava flows and scoria deposits. In addition to field observations, lidar DEM and reflection intensity data were used to identify specific surface features, such as recently disturbed, undisturbed, lichen covered, and heavily vegetated lava, and tephra, including rafted material from late stage cone collapse.

Preliminary results show that disturbed lava and undisturbed lava can be identified by their low and distinctive lidar reflection intensities, ranging from 30 to 50 and 70 to 80, respectively, on a linear scale of 0 (minimum) to 251 (maximum) arbitrary units. Lichen covered lava and rafted cone material are similarly identifiable in the lidar data, based on their higher reflection intensities of 90 to 105 and 130 to 145, respectively. Due to the very high inherent reflectivity of vegetation in the near infrared wavelength at which the Mokst Butte lidar data was collected, it is often difficult to distinguish surfaces of high reflectivity from surfaces that are heavily vegetated. Specifically, areas blanketed by tephra, which have been shown to have high reflectivity in lidar data, are also typically heavily vegetated, because the tephra provides a good soil base.