Coal Bumps and Odd Dynamic Phenomena - A Numerical Investigation 

Jeffrey K Whyatt Whyatt, J. , Mining Engineer
 

NIOSH Research Laboratory
 

Spokane, Loken, M. WA
 

Marc C Loken, President
 

M&K Consulting
 

Shoreview, MN
 

ABSTRACT 

The Crandall Canyon accident investigation included an 

interesting and unexplained observation by rescuers that the 

“barrier rib had shifted northward as a unit, as much as 10 feet.” 

This is not the first mention of such a movement, although such 

reports are rare. Historical accounts describe unusual movement 

and displacement of intact coal, cribs and timbers. Two movements 

of particular interest are the creation of gaps above coal pillars and 

falling of standing support elements without apparent damage. 

A dynamic boundary element program was used to explore 

movements induced by slip on geologic features removed from 

the affected panel. While the resulting models are much too 

simple to fully replicate these observations, they do show that the 

types of phenomena observed are possible. They can also provide 

insight into the types of motions that ground support elements are 

subjected to during large bump events. This was demonstrated 

for the case of a large bump in a Book Cliffs coal mine. Seismic 

information suggested the source mechanism to be normal slip on 

a fault. A model of that source showed initial dilation of the panel 

followed by dynamic compression and rebound – consistent with 

underground observations. The initial dilation is important as it 

may allow slender standing support to shift or fall. 

INTRODUCTION 

Dynamic motion of mine roof and floor during a major dynamic 

failure event, often called a bump or bounce, is of considerable 

interest to mine safety research at the National Institute for 

Occupational Safety and Health. This is for two reasons. First, 

these motions may provide insight into location and mechanism 

of the event. While recent investigations have benefited from 

impressive advances in satellite subsidence and seismic monitoring 

(e.g. Gates et al., 2008), there is still a paucity of information 

available during both rescue and investigation. Second, the 

physical hazard of many events is posed by the interaction of these 

motions with the coal seam and support elements. Some motions 

may degrade support protection or even exacerbate the hazard, 

a concern raised in a recent Department of Labor investigation 

(Teaster and Pavlovich, 2008). Thus, a fuller understanding of 

these motions may provide important clues for improving the 

selection and design of support subject to dynamic loading. 

This work builds on an observation from a deep South African 

reef gold mine – that energy-absorbing props were found laying 

on the floor, intact, after a rockburst (Napier, 2009). Loken (1992) 

used a dynamic boundary element program to follow the complex 

dynamic response to a sudden extension of an idealized stope or 

panel. This response includes both body and surface waves. In 

an idealized model of this case, Loken showed that a net dilation 

(vertical expansion) precedes closure at certain locations in the 

panel. Such a motion unloads props, allowing them to fall over – 

especially if installed at an angle in a dipping panel or stope. 

This study extends this method of dynamic analysis to events 

driven by slip on geologic features. The paper starts with a review 

of dynamic phenomena that have been observed in coal mines. An 

attempt is made to infer surface movements, and the sequence of 

movements, that might cause the observed phenomena. A simple 

dynamic boundary element program is then described. The 

program simulates production of body waves by simple ground 

motions including slip, the travel of these waves through the 

ground and the conversion of body waves to surface waves at the 

surface of mine openings. Finally, a simple case study is analyzed 

to demonstrate use of the model. 

ODD OBSERVATIONS AND INFERRED MOTIONS 

A small number of observations of odd dynamic phenomena 

have been reported in association with dynamic failure events in 

a few mines. The rarity of these observations suggests that the 

phenomena are also rare, or at least observers rarely report them. 

Another interpretation is that observers may have been confused 

by events. However, recent reporting of such an observation in the 

Crandall Canyon investigation (Gates et al., 2008) suggests that, 

even if rare, these phenomena are real and important. Observations 

from throughout North America were collected and are summarized 

here in a roughly chronological order. 

Johnson Colliery 

Ashmead (1924) reports observations from the Johnson Colliery, 

an Anthracite mine. Generally, he states that “men who have been 

at work in a section where a bump or shock took place state that 

anything and everything in the direct line of the bump is destroyed. 
The direction of the force is marked. One man was walking along 

his room and had one foot in the air in the act of taking a step 

forward when a bump occurred. The only blow that he felt was one 

administered to the foot that was raised in taking the forward step. 

His leg was broken but no other part of his body was injured.” 

Ashmead also provides detailed descriptions, including sketches, 

from three specific incidents. These are: 

1. Two men were mining a pillar when a bump occurred. The 

rescue party found the “roof, floor and ribs, so far as visual 

indications were concerned, in their normal conditions, but 

the cogs, instead of being 10 ft. apart were only 3 1⁄2 ft apart 

yet were intact.” (Figure 1) Track running between the cogs 

(packs) was nearly on edge. Further mining revealed a “channel 

or crevice 5 ft wide at the top and about 2 ft wide at the bottom” 

within the pillar. 

Figure 1. Displacement of packs and track attributed to a bump 

event that also appeared to have created a 1.5 m split in a pillar 

(after Ashmead, 1924). 

2. Men were loading a car during pillar mining. After the accident 

the “roof, floor and ribs appeared to be in normal condition.” 

However, one miner was found lying on top of the car “where 

he had evidently been thrown,” and died as a result. 

3. A miner was driving a gangway through a pillar when a bump 

occurred. Reportedly, “the roof, the floor and the ribs were 

apparently normal, but the end of the mine track was sticking up 

in the air and the miner lying under it.” 

Coronado Mine, 1924 

Rice (1924) also recounts observations from the Coronado Mine 

in Washington State. These include what he called “two remarkable 

manifestations of wave motion.” These are: 

1.	 “the roof was not broken yet a timber crib had been moved from 

the upper side of the entry to the lower side and was intact and 

tight to the roof” 

2. “at the lower side rib, over the coal which had been crushed 

down 4 or 5 inches, there was a space between it and the solid 

roof which extended in 3 or 4 ft.” 

Springhill No. 2 Mine 

Rice (1924), in a detailed history of bumps at the Springhill No. 

2 Mine, includes an account from a bord “where a pack or crib 7 

feet high made of 4 foot sticks had been built on the high side [of 

an entry driven on strike]. After the bump, this crib was found tight 

against the low side with not a stick displaced.” 

Herd (1930) described district bumps that “caused large-scale 

destruction of the levels ahead of the longwall face but no damage 

to the face itself.” In each case, the “lower part of the coal seam 

was extruded bodily up-dip into the upper level.” 

McCall (1934) updated Herd’s descriptions of Springhill Mine 

observations, including particular instances. In the first (Figure 2), 

“all east side chocks in this place have been moved about two feet 

westward.” 

Figure 2. Section of a timber pack displaced as a unit during a 

coal bump (after McCall, 1934). 

Also, with few exceptions, “individual sticks have not 

been displaced.” Finally, “the booms and the collar boom which 

supports the booms between chocks have not moved but the lower 

portion has moved as a unit.” In the second location, this same 

event displaced empty and full mine cars without other damage 

(Figure 3). 

Notley (1980) describes two unusual phenomena observed 

during the long history of bumping at Springhill (with reference 

to some of the observations described above). Both occurred with 

minimal roof disturbance. These are: 

1.	 “a sudden extrusion into the mine openings of solid sections of 

the coal seam” 

2.	 “bodily movement of timber packs without disturbing their 

structure” 

In the case of movement of intact blocks of coal, Notley 

elaborated further, describing how the top 14 inches of coal usually 

remained attached to the roof and that separation occurred along a 

well-defined parting in the coal seam. In addition, the “displaced 

coal often retained its structure, requiring as much cutting force in 

recovery operations as in original mining.” 

Greene (2003) provides a historical account of the 1958 bump 

disaster. This account includes description of a miner’s arm 

becoming entrapped in a timber pack during the event. According 

to Greene (p. 50), the pack “bounced apart and then came together 
with Rector’s elbow area flattened between two beams” of the 

recompressed pack. 

Figure 3. Displacement of mine cars by a coal bump (after 

McCall, 1934). 

Book Cliffs, 1993 

Boler et al., (1997) investigated a 1993 failure event in the Book 

Cliffs Coal Mining District of Utah that produced a 3.6 magnitude 

seismic event. Underground, the bump destroyed several pillars. 

Coal expelled from pillars filled entries and partially buried miners. 

After the bump, “pillars were crushed and became piles of broken 

coal, such that over the entire damaged pillar array there was no 

longer any contact between roof and crushed pillars. The roof 

remained substantially intact and suspended above the pillar array 

with negligible closure (p. 21).” Timber support was also observed 

to be affected as follows: 

“Support timbers were broken in compression, maintaining 

roof-to-floor contact and indicating roof-to-floor convergence 

of a few centimeters (estimated from photographs of support 

timbers that were broken in compression). Support timbers were 

displaced relative to wedges that hold them in place indicative of 

roof-to-floor shearing motion or roof-to-floor vertical opening that 

allowed timbers to partially fall and retrap. With roof-to-floor 

shearing, neighboring timbers might be expected to show consistent 

orientation of horizontal offset. Because neighboring timbers 

were observed to show random directions of horizontal (if any) 

motion, the vertical opening with retrap scenario is more likely.” 

Crandall Canyon, 2007 

Gates et al., (2008) reported observations made during efforts to 

re-establish the No. 1 Entry. The first of these was that “as loading 

advanced inby crosscut 123, rescuers observed that part of the 

barrier south of the No. 1 entry had moved northward as a result of 

the August 6 ground failure. The barrier rib had shifted northward 

as a unit, as much as 10 feet. In some areas, the displaced barrier 

slid along the immediate roof and tore loose the original roof mesh” 

(see Figure 4). “In other areas, the immediate roof was carried 

northward and damaged the original installed roof bolts” (Figures 

4 and 5). 

Figure 4. Damaged roof bolts and torn mesh after August 

6 accident resulting from northward movement of southern 

barrier (after Gates et al., 2008). 

Figure 5. Damaged roof bolts in No. 1 entry after August 6 

accident resulting from northern movement of southern barrier. 

Mesh shown was installed during rescueoperations, over 

damaged original bolts. Camera view is indicated by arrow in 

index map insert (after Gates et al., 2008). 

One crosscut further inby (#124), the condition of displaced 

coal is described as follows (p. 23 of Gates et al., 2008). “The 

No. 1 entry was packed with rubble the full width and height of 

the original mined opening. The continuous mining machine was 

loading from a rubble pile that resembled an unmined coal face.” 

Movements may have continued during the rescue operation. An 

observation in one inspector’s notebook “following a bounce that 

occurred on August 15th, that it appeared that the tops and bottoms 

of the Rocprops had moved” was reported by Teaster and Pavlovich 

(2008). 

Gate et al., (p. 27) described a “void up to 20 feet deep into 

pillar at the roof line” (see Figures 6 and 7) created by the bump 

that ended rescue efforts. Gates et al., also mention that “coal 

was thrown violently across the No. 1 entry.” And finally, that 

this “dislodged coal threw eight RocProps, steel cables, chain-link 

fence, and a steel channel toward the left side of the entry, striking 

rescue workers and filling the entry with about four feet of debris.” 

One injured miner was found “entangled in chain-link fencing.” 
Figure 6. Damage to outby portion of pillar on right side of No. 1 

entry, outby August 16 accident site (After Gates et al., 2008). 

Figure 7. 20-ft deep void over pillar on right side of No. 1 entry 

following August 16 accident (After Gates et al., 2008). 

Interpretation 

These observations are difficult to fully interpret and many 

appear to have confounded observers. However, a few key 

characteristics of ground response to dynamic failure are evident. 

These characteristics are “provisional” at this point, because they 

are based on a small number of observations; and also because these 

motions, and their necessary conditions, are poorly understood. 

These characteristic motions include the following. 

- Dynamic Closure and Gaps 

First, and most common, is overshooting of seam closure where 

roof is strong and remains intact. The full dynamic compressive 

load drives failure in the coal and/or floor that effectively shortens 

segments of coal seam, leaving a gap between coal and roof upon 

rebound. 

- Dynamic Opening and Slender Support 

Observations of props falling over in a South African gold 

that motivated this work are similar to reports from coal mines, 

particularly the Book Cliffs event (Boler et al., 1997) and possibly, 

props in the Crandall Canyon rescue event. Standing support that 

will not stand without axial loading appears to be vulnerable to any 

surface motion that includes dilation of the mined opening. 

- Dynamic Lateral Movements 

A number of observations include lateral movement of objects. 

In many cases such movement is unlikely to be noted as the original 

position is uncertain. However, movement of rail cars relative to 

(and off) the track is a clear indication, although such movements 

are likely accompanied by vertical motion. 

- Complex Dynamic Motions 

More complex motions, including sequences of lateral and 

vertical motions, are likely needed to explain movement of objects 

in contact with roof and floor, including packs and intact sections 

of coal seam. Clearly, dilation is needed to remove clamping and 

thereby frictional forces that would resist movement and disorder 

the moving object. Downward movement of the floor as part of 

this dilation would help explain how clamping due to object weight 

might be removed and how a timber pack might open up. Lateral 

movements immediately before dilation might impart a lateral 

velocity. Regardless, though, an adequate explanation of such 

complex motion rests on an understanding of the simpler motions 

described above. 

DYNAMIC BOUNDARY ELEMENT MODEL 

This study simulated observed surface motions of coal seam 

roof and floor as a linear elastic problem in dynamics. In such a 

problem, movement is instigated by simple source, like shear on 

a plane (fault). The effect of the disturbance is traced through an 

elastic, homogeneous medium containing mine openings. The 

simulation includes both body waves propagating between source 

and coal panel, and surface waves propagating along the surfaces, 

primarily roof and floor, of the panel. As such, the simulation 

entirely ignores geology. However, it is three-dimensional since 

sources are locations, not lines, and may be located randomly with 

respect to a panel. 

The boundary element method (BEM) chosen has two distinct 

advantages over volume-based (finite element and finite difference) 

methods for these highly idealized simulations. First, BEM 

requires discretization of source and mine surfaces only – not the 

entire rock mass volume – a significant shortcut in both formulating 

and solving problems. Second, the BEM formulation automatically 

satisfies the correct boundary conditions at infinity (radiation 

conditions) without further formulations (dynamic boundaries). 

The FORTRAN BEM program SLIP (Loken, 1992) was 

resurrected, updated and revised for this project. This program is 

a numerical implementation of Maruyama’s three-dimensional 

displacement discontinuity solution in elastodynamics (Maruyama, 

1963). The program was developed for the Chamber of Mines 

Research Organization in the 1990’s to investigate rock burst 

behavior in deep underground mines in South Africa. The program 

is capable of investigating elastodynamic effects from a variety of 
sources, including point, crack, and volume sources in an infinite 

domain. The program was modified to include the following 

features (1) inclusion of traction free surface elements so that body 

waves produced by remote dynamic sources become surface waves, 

(2) extension of boundary types and shapes (stopes and/or cracks 

using quadrilaterals and triangles), (3) estimation of failure at 

prescribed locations, and (4) video sequences of time-space output 

results in prescribed “field-point” windows. 

TEST CASE: INFERRED MOTIONS AND

 POSSIBLE SOURCES
 

The Book Cliffs case study by Boler et al., 1997, reviewed 

previously, provides a convenient test case. Seismic records 

analyzed by Boler et al., indicated slip on a normal fault somewhere 

above the damaged panel, most likely in the overlying Castlegate 

Sandstone, was the most likely cause (Figure 8). 

Figure 8. Preferred failure mechanism for the Book Cliffs mine case 

proposed by Boler et al., (1997). 

A simple model of this geometry was formulated, consisting of 

a slip surface with a sudden shear displacement and a simple panel 

without pillars (Figure 9).

Figure 9. Simplified model geometry. Closure was tracked at point #1, 

located at the midpoint of the panel. 

The assumed material properties of the elastic 

medium were: mass density ρ = 2700 kg/m3

, longitudinal wave velocity 

α = 5367 m/s, and transverse wave velocity β = 3267 m/s. The boundaries 

of the fault surface and the mined opening were approximated by equallysized square boundary elements of dimension 3 m by 3 m. A 1 m slip was 

assumed. While this value is relatively large, it’s convenient for scaling 

results to any desired slip magnitude. That is, a 10 cm slip would realize 

10% of the modeled motion. The total simulation time was 0.5 s, using 

200 time steps of equal time step length (0.025 s). 

The calculated relative displacement history (closure) at the 

center of the panel is plotted in Figure 10. 

 

 

Figure 10. Calculated dynamic closure and ride (relative lateral 

displacement) between roof and floor at mid-panel. 

It consists of an initial 

dilation followed by closure to a short-lived maximum and then 

rebound to the static closure value. Dilation, or opening of the panel, 

is roughly 15% of maximum dynamic closure and nearly half the resulting 

static closure. Relative horizontal displacement (ride) is also plotted. Ride is 

very small during initial dilation but is significant at later times. 

This pattern correlates well with the in-mine observations 

reviewed earlier. Recapping, these were (1) dilation of the coal 

seam that temporarily freed timber props without strong lateral 

movement and (2) dynamic compression of pillars by an elastic 

roof that rebounded from its maximum closure, leaving a gap 

between pillar remnant and roof. Boler et al.’s inference that 

movement between timbers and wedges indicated dilation before 

compressive “retrapping” of the timber-wedge column is consistent 

with figure 11; thus the model captures both the observed behavior 

and their inferred order of occurrence. The sensitivity of this result 

to changes in the location, orientation and sense of slip is being 

examined. 

SUMMARY AND CONCLUSIONS 

This review of odd observations of dynamic behavior during 

coal bumps showed there are consistencies, despite the apparent 

fantastical nature of some accounts. Carefully documented cases 

from the Book Cliffs and Crandall Canyon provide added credence 

 

to historical descriptions. The existence of these cases may 

encourage increased reporting of similar phenomena. 

A dynamic boundary element program was developed to 

examine these phenomena. While the full complexity of these 

movements has yet to be modeled, a simple model of one 

case succeeded in showing that the proposed normal fault slip 

mechanism (based on analysis of seismic data) was consistent with 

underground observations. These observations include apparent 

movement of timbers relative to wedges – suggesting a period of 

initial dilation – and creation of spaces above crushed pillars – 

consistent with dynamic closure of the seam followed by rebound. 

These movements are also consistent with a number of the other 

cases reviewed. 

Commonalities in historical cases and initial computational 

results suggest that these odd dynamic observations, including 

apparent movement of intact barrier pillar remnants at Crandall 

Canyon, cannot be discounted. Indeed, they may provide important 

insight and constraint to source mechanisms. They also provide 

insight into complex dynamic loading that may be exerted on 

mine support. One aspect of this loading, the possibility of net 

dilation of the panel, is particularly important to the performance 

of support that relies on clamping forces for stability, like slender 

standing support. Such support is inappropriate for some dynamic 

failure mechanisms and mine geometries. The full range of such 

conditions remains to be defined. 

Ongoing work is aimed at improving modeling capabilities 

and simulating more complex movements. It aims to confirm the 

validity of more of these odd observations. It also aims to explore 

what these observations imply about source mechanisms, damage 

mechanisms, and appropriate design of dynamic support elements. 

REFERENCES 

Ashmead, D. (1924). Bumps and Shocks Disturb Johnson Colliery. 

Coal Age, November 6, 1924. pp. 641-643. 

Boler, F., S. Billington and R. Zipf (1997). Seismological and 

energy balance constraints on the mechanism of a catastrophic 

bump in the Book Cliffs Coal Mining District, Utah, USA. Int. 

J Rock Mech. Min. Sci. Vol. 34, No. 1, pp. 27-43. 

Gates, R., M. Gauna, T. Morley, J. O’Donnell, Jr., G. Smith, 

T. Watkins, C. Weaver and J. Zelanko (2008). Report of 

Investigation — Fatal Underground Coal Burst Accidents, 

August 6 and 16, 2007, Crandall Canyon Mine, Genwal 

Resources Inc, Huntington, Emery County, Utah. Department 

of Labor, Mine Safety and Health Administration, ID No. 42-

01715, 472 pp. 

Greene, M. (2003). Last Man Out: The Story of the Springhill Mine 

Disaster. Harcourt, NY, 342 pp. 

Herd, W. (1930). Bumps in No. 2 Mine, Springhill, Nova Scotia. 

AIME Trans., 88, 151-191. 

Loken, M. (1992). A Three-Dimensional Boundary Element 

Method for Linear Elastodynamics. Ph.D. thesis, University of 

Minnesota, 237 pp. 

Maruyama, T. (1963). On the Force Equivalents of Dynamical 

Elastic Dislocations with Reference to the Earthquake 

Mechanism. Bulletin of the Earthquake Research Institute, Vol. 

41, pp. 467-486. 

McCall, T. (1934). Further Notes on Bumps in No. 2 Mine, 

Springhill, Nova Scotia”, AIME Trans., Vol. 108, pp. 41-70. 

Napier, J. (2009). Personal Communications. 

Notley, K. (1980). Analysis of the Springhill Mine Disaster 

(October 23, 1958), Ph.D. dissertation, Queen’s University, 185 

pp. 

Rice, G. (1924). Occurrence of Bumps in the Springhill No. 2 

Mine of the Dominion Coal Company, Limited, Department of 

Public Works, Nova Scotia, Office of King’s Printer, Halifax, 

Nova Scotia, 78 pp. 

Teaster, E. and J. Pavlovich (2008). Independent Review of 

MSHA’s Actions at Crandall Canyon Mine Genwal Resources, 

Incorporated Huntington, Emery County, Utah. Mine Safety 

and Health Administration report, 46 pp. Available at: http:// 

www.msha.gov/CCreview/CrandallCanyonIRComplete.pdf