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At least 10 distinct flows of obsidian were produced by volcanism of the MEVC, some of which were exploited by indigenous peoples in prehistoric times to make tools and weaponry. The first magmatic cycle took place between 7.5 and 6 million years ago and is represented by the Raspberry , Little Iskut and Armadillo formations, each of which is ...
Another possible cause may be the impact that formed the Wilkes Land crater in Antarctica, which is estimated to have occurred around the same time and been nearly antipodal to the traps. [11] The main source of rock in this formation is basalt, but both mafic and felsic rocks are present, so this formation is officially called a Flood Basalt ...
Before a storm that can potentially nucleate debris flows, forecasting frameworks can often quantify the likelihood that a debris flow might occur in a watershed; [18] however, it remains challenging to predict the amount of sediment mobilized and therefore, the total size of debris flows that may nucleate for a given storm, and whether or not ...
This site is on and in late middle-Pleistocene fanglomerates (now-cemented alluvial debris flow deposits) known variously as the Calico Hills, the Yermo Hills, or the Yermo formation. Holocene evidence includes petroglyphs and trail segments that are probably related to outcrops of local high-quality siliceous rock (primarily chalcedony in ...
Tephra is a generalized word for the various bits of debris launched out of a volcano during an eruption, regardless of their size. [4] Pyroclastic materials are generally categorized according to size: dust measures at <1/8 mm, ash is 1/8–2 mm, cinders are 2–64 mm, and bombs and blocks are both >64 mm. [5] Different hazards are associated with the different kinds of pyroclastic materials.
The 1st to 13th lobes were named in the order they were formed. Collapsing of the lava dome began to occur when the lobes, pushed out by the newly supplied magma, started to give way on the slope, causing a phenomenon known as pyroclastic flows (in which debris and volcanic gasses flow down the mountainside at speeds of 100 km/h).
The evolution of life in this time reflected the conditions created by the assembly of Pangaea. The union of most of the continental crust into one landmass reduced the extent of sea coasts. Increased erosion from uplifted continental crust increased the importance of floodplain and delta environments relative to shallow marine environments.
These layers settle on the land and, over time, sedimentation occurs incorporating these tephra layers into the geologic record. Tephrochronology is a geochronological technique that uses discrete layers of tephra—volcanic ash from a single eruption—to create a chronological framework in which paleoenvironmental or archaeological records ...