This story is about an Earth mound that we suspected was a grave, the mysterious events that were reported about it, and our investigation of it. That was many years ago, and I no longer am sure of all of the exact details, but I think that I have the story pretty much right. It was a good adventure, and some times it was scary! I still am curious about it, and maybe somebody here can suggest another approach for investigation.
In a remote mountain camp that I used to frequent, legend said that some places were sacred to the people who lived in that region long ago. I don't know how true those legends were; I suspect that at least some of them were made up just to entertain the campers and keep our interest alive so that we would return.
One supposedly sacred place was a mound of Earth about the size of a large grave, and less than a foot high. It was beside a little-used trail that led out of the camp. Legend said that one night many years ago, some adult and youth campers were returning to the camp along the trail, and they saw a strange light floating above the mound, and they heard muffled voices apparently coming from the mound. That story scared the wits out of some of the other campers, and it sparked an interest in still others. Several people looked at the mound after that, and supposedly a few people actually saw the light and heard the muffled voices. They also claimed that the mound surface occasionally rose and fell quite noticeably. The director said that the mound was a grave, and he told people not to tamper with it. When the director heard that some people were planning to dig up the mound, he threatened to expel anybody who desecrated it.
I tried long and hard to find out whether any of the legends were true, and especially to find details of the mysterious light and the voice-like sounds at the mound. Was the light just shining on the mound, or was gas burning at the surface of the ground, or was some sort of luminous gas cloud hovering over the mound? Was the light stationary or moving? What color was the light, and how bright was it? Were the color and intensity steady or varying? Were the voice-like sounds audible away from the mound, or did the observers have to put their ears to the surface of the mound to hear anything? I heard so many conflicting stories that obviously I couldn't believe any of them. And some times my questions were met with stony silence.
Later, the camp had a legal problem that required the camp boundary to be surveyed and marked. The survey was started by one of us who was a civil engineer, with one of his sons who was a student in civil engineering, and me. At the boundary corners where there were no existing survey monuments, and at many other points along the boundary, we set monuments which we drove deep into the ground for permanence and stability.
On the first week-end of the survey, we reached the mysterious Earth mound, and found that one of the camp boundary corners was at the edge of the mound. The engineer declined to drive a survey monument into the ground so close to the mound; he wouldn't even let us step on the mound, or disturb it in any way. He must have been serious, because he went to the considerable extra work of treating that boundary corner as inaccessible. That involves setting extra monuments in the vicinity, measuring to them, computing their positions, and recording all of those extra monuments and measurement data on his map.
We couldn't finish the survey in one week-end. So a few weeks later, the engineer's son, I, and another person, returned to the camp for several days to work on the survey. We were curious about the mound, so we took what instruments we had available, to investigate it. The instruments included a flammable gas detector, a metal detector, a magnetic locator, a pipe and cable locator and tracer, and an acoustic leak detector.
To avoid stepping on the mound, we made tong-like devices so that one of us could stand on each the side of the mound while we gently held the instruments on the surface of the mound. Thus we did not desecrate the mound.
Mysterious lights some times are caused by burning or glowing methane gas from decaying organic material. It goes by various names like swamp gas and will-o'-the-wisp. If the mound really was a grave, then (hopefully!) all buried organic material had decayed long ago, and no longer was producing gas. Possibly methane gas was coming from decaying vegetation on and under the ground surface. We thought that if methane was present in sufficient quantity to burn or glow, and thus produce the mysterious light, then probably our gas detector would show it. We could not account for the lights in any other way, as the mound was far from all roads, automobiles, buildings, electric wires, machinery, and other people. Later, I found that some flammable gas detectors respond only to particular tracer-gasses, and I am not certain now whether our detector was of that type. (For example, some commercial natural gas contains a tracer-gas, or odorizer, so that in case of a leak, people can smell the gas.) At the time of the investigation, I did not know to ask that question.
The acoustic leak detector was made for detecting leaks from buried pipes; to use it, normally one pushed a long probe into the ground, and listened in various frequency ranges for a hissing sound. Rather than push the long probe into the mound, we used a surface probe so that the acoustic detector functioned somewhat like a stethoscope but was much more elaborate and sensitive. The surface probe was not as sensitive as the long immersion probe, but it seemed better than nothing.
We also took a level; that is a delicate optical instrument that includes a telescope with cross-hairs. The instrument is clamped to a heavy tripod and is used to sight along a level line past the cross-hairs, to an elevation measuring rod that is held vertically on the ground where the elevation is to be measured. We temporarily marked several points on the mound surface without penetrating the ground or even disturbing the surface, and we also marked several control-points at various distances from the mound for comparison.
Since the camp was not in use during the time of our survey, we left the level instrument set up on its tripod, protected from the elements, several feet away from the mound, and we frequently measured the elevations of our marked points on the mound relative to our control-points.
Night-time level measurements were especially clumsy, as one of the two rod-men had to hold not only his end of the tongs, but also a flash-light to illuminate the right part of the elevation rod, while the instrument-man had to hold another flash-light to illuminate the telescope cross-hairs in the level instrument.
To observe the mound as much as possible, we camped on the trail beside the mound. When-ever anybody woke during the night, he looked for the lights, tested for flammable gas, listened with the acoustic detector, looked for obvious change in the mound surface elevation, and recorded the results and the time of his observations. If two people were awake at the same time, then they woke the third person, and we measured the elevations of our marked points with the level instrument.
We never saw the mysterious lights, and we never detected flammable gas. We suspected that the stories about seeing the lights, were just stories, perhaps from the active imaginations of some young campers who already were a bit spooked by the darkness, or who decided to have some fun by spooking other campers.
We never found any indications with the metal detector, magnetic locator, and pipe and cable locator. Unfortunately, those instruments were affected noticeably by the survey monuments that we had set near the mound during the first week-end of the survey. But at least our instruments showed that there were no massive electrical conductors and no ferromagnetic materials under the ground, and no metal pipes or electrical wires in the vicinity. There were no noticeable changes in any of the indications of those instruments; if any of them had shown sudden changes while we watched, then we *really* would have been shaken! Imagine yourself holding an instrument over a mound that you suspect of being a grave, and seeing indications of something moving under the ground! No thanks!! But this was kind of weird; we half-wanted to find something, and yet we were afraid of finding anything. I suppose that's one of the hazards of such an investigation. The acoustic detector did shake us up! During the day-times, the mound was quiet; but at night, often we heard what sounded like muffled conversation, some times apparently quite heated as in a vehement argument.
No words were intelligible to us, but that seemed reasonable because the early inhabitants of that region did not speak English. We were fairly sure that the sounds were not caused by wind in the trees, or by the nearby river, as those sounds, at least in the audible frequency range, had very different characteristics. Furthermore, the sounds seemed to be independent of the wind. We were unable to identify any other sources of sound that matched the apparent inflections and other characteristics of the supposed voices, although we could not rule out other sources completely. We searched with the acoustic detector at many points around the mound and for some distance in both directions along the trail, particularly with the thought that we might be hearing under-ground water flow or its effects. But we never heard the voice-like sounds except right on the mound, and there was no indication of moving ground-water even on the nearby steep river bank. We thought that if much ground-water were present, then probably we would see a spring on that steep bank. And if the wind or the river or other natural processes were causing the sounds, then presumably we would have heard the sounds at points away from the mound, and also during the day-times. But we didn't; we heard the sounds only right on the mound, and only at night.
At first, the sounds alarmed us, almost to the point of running for our lives when the arguments seemed to grow so fierce that we half-expected ghosts to come flying out of the mound! But if the sounds really were voices, then apparently the talkers did a lot of arguing and not much else. Those "voices" sure sounded real!
The level instrument gave us the most definite, and rather alarming, indications. The mound surface elevation, relative to the surrounding ground, varied by several tenths of a foot throughout the day and night. For such a small ground area, that is a lot of elevation change. Usually, the mound was higher at night. The elevation changes were greatest at the center of the mound, and decreased to zero at the edges of the mound. All of our peripheral control-points were rock-stable in elevation. Even during several hours of observation while we were in the camp, we never actually saw the mound elevation change; it just was different when we returned for the next measurement. And we did not notice any correlation between the voice-like sounds and the elevation changes; if there was a common cause for the sounds and the elevation changes, then at least part of the effect was delayed. Since we were using a high-quality level and were experienced in using it, and since all of our control-point elevations were stable, we believed that the mound elevation changes were real, not the result of motion of the level instrument itself or errors in measurement.
Ground surface elevation can be affected by ground-water, as in subsidence in some areas where the ground-water is depleted by pumping from wells. But such changes generally do not cycle over a period of only one day. Even ocean tides can affect the nearby ground surface enough to be detected with good instruments, but that did not apply here. Furthermore, I would not expect such change to be so localized.
If we ever had seen the mound surface suddenly lurch upward, then probably we would have fled in panic, and thought about retrieving the instruments and our camping gear later. But the elevation never changed while we were watching. We did have some uneasy moments during the elevation measurements; some times, to the observer looking through the telescope of the level instrument, the elevation rod appeared to rise. But that always turned out to be instability in holding the rod on the mound with the make-shift tongs that we were using in order to avoid stepping on the mound. That was clumsy at best. And night-time measurement was especially clumsy because of the need to hold the flash-lights.
We had a scare one night when the instrument-man thought that the mound elevation was changing right before his eyes. It turned out that he had forgotten to focus the telescope properly, and he was seeing parallax error as he moved his head. An instrument telescope generally has two focusing adjustments, and if both of them are not set properly, then the elevation rod can appear to move with respect to the cross-hairs. While the instrument-man was illuminating the telescope's cross-hairs with a flash-light, his head was moving vertically. Fortunately, before we panicked too much, he happened to move his head horizontally, and recognized that he was seeing parallax error. When he made the two focus adjustments, the "motion" disappeared. We breathed easier after that.
The mound elevation changes remained a mystery to us; we never did figure them out.
