Jordan craters Essay Example For Students

Jordan craters Essay The Jordan Craters volcanic field is located on the Owyhee-Oregon Plateau at the southeastern end of a series of young basalt fields extending from near Bend, Oregon, through Diamond Craters in south-central Oregon (Volcanoes of the World). The Jordan Craters field is limited to the northern most and youngest portion of a larger (250 square kilometers) Quaternary alkaline basalt field. There are three major vent areas aligned north to south along surficial and inferred expressions of the regional Basin and Range faulting (Hart, W.K., and Mertzmann, S.A. ). Fluid pahoehoe basalt flows emanated from each of these sources, with pyroclastic activity confined to small scatter cones and to a larger crater-cone complex (Coffeepot Crater) at the northernmost edge of the Jordan Craters portion of this field (Volcanoes of the World). This entire Quaternary alkaline basalt field is part of a larger field (nearly 800 square kilometers) that includes Pleistocene and Pliocene olivine tholeiite to transitional basalt flows and vents. Jordan Craters is a wonderful sight mainly because of its well-preserved vents and striking flow features. Near Coffeepot Crater, the flow surfaces are vesicular shelly pahoehoe, which grade to massive tube-fed ropy pahoehoe in the distal regions. A 75-square-kilometer coffeepot Crater is a heart-shaped tephra cone constructed of numerous overlapping lobes of alternating densely to weakly welded scoriaceous lapilli and bombs (Volcanoes of the World). The walls of the crater show good evidence for a fluctuating lava pond, which appears to have broken through and rafted away portions of the northeastern and southeastern crater walls. Backflow of the lava pond into the conduit is indicated by pahoehoe crust on the present crater floor. The Jordan Craters lava flow field is mineralogically and chemically homogeneous, whereas proximal tephra and flow deposits exhibit significant chemical heterogeneity which correlates with the eruptive history. Also noteworthy are the many excellent examples of basalt flow and eruption features, including ropy and shelly pahoehoe surfaces, lava channels, lava blisters, pressure ridges and squeeze-ups, pit craters, lava-tube skylights, vertically striated internal crater walls, and re-fused cobbles of rhyolitic country rock. Additionally, the southeasterly flowing lava altered ancestral drainage patterns, giving rise to a natural dam and the formation of two small lakes (Upper and Lower Cow Lakes). The Jordan Craters field is located on a high plateau approximately 200 kilometers southwest of Boise, Idaho.