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<br />Memorandum to Kathy Welt <br />Ausust 28, 1997 <br />Page 4 <br />9,I0,1I. The next three crack azeas visited (a, b, and c) aze located in Gribble Gulch <br />about 3000 feet east of Muffler Rock in the SYz, Section 19. Numerous seeps <br />were observed amidst hummocky topography. These cracks, which all trend <br />roughly north-south, were first observed earlier this summer. The loagwall face <br />in Panel 3 passed beneath this azea in December 1997. <br />a) The cracks aze as much as 1-foot wide and 1-foot deep. We passed by a <br />number of seeps enroute from the west. <br />b) These cracks aze located beriveen two seep azeas. Some cracks show <br />offset, and aze as much as 1-foot wide and 1 %-feet deep. The cracks are <br />located in an area that appears to have been raised up (bulged) a foot or <br />more. <br />c) Some of these cracks aze displaced as much as 1 foot and aze up to 1- <br />foot wide and deep. <br />12. Small stream and seep azea: This area is located about 500 feet N30°E of the <br />toe of the landslide at Muffler Rock. A streamflow of 5 to 10 gpm is estimated; <br />significantly more than Dave has observed during the last few yeazs, and <br />roughly 3 to 4 times the flow that I observed in the late 1970x, when mapping in <br />this azea. <br />13. We stopped at the crack area on the ridge north of Apache Rocks in the NW'/<, <br />NW'/< of Section 22 on the way back to the mine. Gary Witt and I observed this <br />crack during our subsidence crack survey in October 1994. The portion of the <br />crack, which trends about north-south neaz the road, where it is founded in <br />sandstone bedrock, looks similaz to the way it looked neazly three yeazs ago. <br />However, little or no trace of the crack can be seen where the crack trends about <br />N30°E beneath colluvium and soil covered with scrub oak, except for a hole <br />about 2%x fee[ in diameter, where the overlying surficial material has trickled <br />down through the underlying crack in bedrock. <br />Summary of Crack Occurrences and Landslide at Muffler Rock <br />With the exception of crack azea examined at Location 2, all the cracks observed on the north <br />side of Jumbo Mountain occur in hummocky topography typically caused by landslides. <br />With the current abnormally high moisture conditions, continued mass-gravity movements <br />aze likely. The cracks were likely caused mainly by landslide movements in pre-existing <br />slide azeas due to increased moisture this spring. However, these landslide movements may <br />have been influenced or accelerated to some small degree by longwall mining activities. <br /> <br />