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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 69 (1985)

Issue: 2. (February)

First Page: 285

Last Page: 286

Title: Recent Armored Mudballs Associated with a Mudflow, Egan Range, Eastern Nevada: ABSTRACT

Author(s): Ronald R. McDowell, Jay E. Valusek

Article Type: Meeting abstract


Armored mudballs and boulders (AMBs) were observed in direct association with a mudflow produced by heavy snowmelt and rainfall in the spring of 1983. The mudflow was 0.8 km wide, about 2 km in length, and up to 23 cm in depth. The mudflow followed an ephemeral stream channel and moved downstream with force sufficient to bend over evergreen trees up to 90 cm tall.

End_Page 285------------------------------

AMBs ranged from 5 to 90 cm in diameter and were spherical to ovoid with alternating internal layers of clay and limestone clasts (lithologically identical to stream gravels). AMBs were most commonly found lodged in the upper 1-3 cm of the mudflow; a few lay in the stream bed adjacent to or downslope from the flow. The majority of AMBs were concentrated near the toe of the mudflow. AMBs appeared to have been produced by a combination of rolling along the stream channel and "rafting" by the mudflow.

Observation of the mudflow and AMBs after 10 hr of steady rainfall revealed the mudflow to be intact, but all except the largest AMBs were reduced to piles of limestone clasts lying on top of the mudflow.

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Copyright 1997 American Association of Petroleum Geologists