AN EXAMINATION OF BASALT LAVA FLOW PEPERITE ASSOCIATED WITH DOTSERO CRATER, COLORADO

The interaction of magma or lava flows with unconsolidated or wet sediment can form breccias and peperites. The study of peperite provides a deeper understanding of the variations in explosive and nonexplosive processes that can be associated with phreatomagmatic eruptions of maar volcanoes. The recognition and study of peperite can provide information on the conditions of the sediment at the time of eruption. The Dotsero maar volcano, located in Colorado, is one of the youngest known intraplate volcanoes in the United States and produced deposits associated with both magmatic and phreatomagmatic processes. The eruption (4,150 years +/- 300 years) occurred with a north-northeast trend, building scoria cones that ascend the North canyon wall of the Eagle River. The resulting lava flow issued southward from a gulch and buries around 0.7 km² (168 acres) of the adjacent flood plain.

This study focuses on the peperite formations from the resulting southward lava flow from the crater rim of the Dotsero maar volcano. Field sites were selected based on maps of the geology, topography, and access. Specifically, study sites include the Eagle Valley Evaporite gypsum deposit exposed along the Dotsero lava flow. The fieldwork for this study consists of recording the sizes of clasts in the peperite located at each of the sites for comparison and the associated identifiable clustering patterns. Distance measurements from the lava flow into the sediment where the peperite is found and location along the flow are also included. Samples of peperite clasts with surrounding host sediment were collected from the sites for further analysis and comparison. The laboratory analysis of the samples collected from Dotsero will include an examination of thin sections and X-ray diffraction. Measurements taken from these analyses will allow for a greater understanding of the sedimentary conditions associated with the interactions that occurred from the Dotsero lava flow and allow for the discernment of the temperature and viscosity of the lava when it interacted with underlying sediments.