Mountain or No Hill? : New Technology May Settle 7-Year Debate About Existence of Palmdale Bulge

When its existence was first announced 10 years ago, the Palmdale bulge, a purported periodic swelling of the Earth north of Los Angeles from Ventura County to the Mojave Desert, generated headlines and predictions of a great earthquake.

When a UCLA geologist claimed three years later that the Palmdale bulge did not exist, that it was an illusion created by faulty data, the phenomenon seemed to fade away, leaving in its wake an atmosphere of doubt.

One headline read: “. . . new study turns geological ‘mountain’ into molehill.”

Actually, the battle over the Palmdale bulge was never won or lost.

Two geologists--Robert Castle at the U.S. Geological Survey in Menlo Park, who discovered the bulge, and David Jackson at UCLA--have been locked in a stalemated debate for seven years, each with a retinue of critics and supporters.

“Both sides got pretty tired,” Jackson said. “Everybody is sort of on the ropes.”

Although the existence of the bulge is disputed, recent work by USGS geologists seems to be confirming, at least, that the landscape north of Los Angeles is in continual motion, heaving up and down as much as half a foot a year. And new space-based technology may soon put to rest any doubts.

If the bulge turns out to be real, and not a phantom result of imprecise measurement, as Jackson contends, the periodic swelling--although only a foot or less in height--may be linked to seismic events such as the destructive Sylmar earthquake of 1971 and Tuesday’s moderate temblor in Palm Springs, Castle said.

Its behavior could also provide important clues about the structure of the San Andreas Fault. This 600-mile-long scar, where two shifting sections of the Earth’s crust are in perpetual collision, is the predicted source of the “Big One,” the devastating earthquake that geologists say is likely to hit the Southland in the next few decades.

Even Jackson agreed. “It would tell us a lot about how the Earth works and stresses build up,” he said. “If it were real,” he quickly added.

The battle of the Palmdale bulge provides a good view of the long, painful course that a scientific theory must run before it becomes established as a scientific fact.

Castle’s discovery of the bulge came in the wake of the Sylmar earthquake. He was conducting a post-earthquake study of the San Fernando Valley that included analysis of old measurements of elevations across the Valley and north and east into the desert.

Castle said he noticed many changes in elevations in the 10 years leading up to the earthquake, with a particularly dramatic change in the “tilt”--the difference in elevations--between Saugus and Palmdale.

8-Inch Tilt

From 1961 to 1964, the tilt between the two towns, just 18 miles apart, appeared to change by more than eight inches. In the geological scale of things, where a mountain range might rise the width of a fingernail in a year, this finding was startling, Castle said. Palmdale appeared to be sitting on top of a bulge in the Earth.

Along with other USGS scientists, he began to examine surveys of the region from as far back as 1902. The result was a picture of an area thousands of square miles in extent--rising around Santa Barbara in the west and descending again east of the Salton Sea--that seemed to have swelled and receded twice, peaking once in 1905 and again in 1974.

Records for the recent bulge were much more complete, Castle said, showing remarkable spasmodic growth, with peaks in 1961 and 1973 as well as local “blisters” and “dimples.” In 1974, the whole region began to collapse like a pierced crust on a fresh-baked pie.

Gone in Some Spots

Currently, measurements of the bulge indicate it has shrunk to a third of its greatest dimensions, with some sections--for instance, the region around Bakersfield--actually lower than they were before the bulge began, Castle said. Even at the time of its discovery in the early 1970s, the bulge was already almost gone. That has been the biggest roadblock to confirming or debunking the phenomenon, Castle said.

“We didn’t recognize the existence of it until it had almost disappeared,” he said.

In 1976, Castle published the first accounts of this “Southern California uplift.” The discovery created a huge stir, prompting a large government study. In January, 1978, 36 teams of scientists fanned out across the region in what Time magazine then called “one of the most extraordinary surveys in the annals of U.S. geology.”

$1.5-Million Study

More than $1.5 million went into the effort to measure the bulge.

“The goal was to try and cover the vast area within a short period of time, producing a detailed snapshot” of the bulge, Castle said.

Ironically, the survey, which was meant to be the final word on the bulge, was marred by some balky equipment and “the worst weather in years.” And that was only the beginning of Castle’s troubles.

Then along came Jackson. In 1979, he started what would become a series of challenges to the Palmdale bulge, most based on flaws in the method used to take its measure.

The job of measuring the finest features of the Earth’s surface is given to geodesists. Periodically, teams of surveyors crisscross an area, charting their course and measuring elevations as they go. The result is a precise contour map.

Antiquated Equipment

A team from the National Geodetic Survey is currently in the middle of the USGS’ annual survey of the region. At last word, they were somewhere around the Cajon Pass, Castle said.

Their equipment is simple and has hardly changed in 100 years: two 3-meter rods marked off in millimeters and a small telescope that is kept horizontal by a leveling device, either a pendulum or a bubble enclosed in a liquid-filled chamber.

A survey team starts out at a point with a known elevation. Many of the lines used to study the Palmdale bulge originated at a bench mark at sea level on the San Pedro waterfront, winding from there along railroad tracks or roads or open country, Castle said.

The rods are usually placed less than 200 feet apart, with the viewing instrument in between. Each rod is viewed through the horizontal telescope. The difference between the heights spotted on each rod denotes the rise in elevation between them. The first rod is then carried beyond the second one and the procedure is repeated--sometimes more than 1,000 times, depending on the distance covered.

Sources of Error Cited

At a professional meeting in 1979 and in a series of journal articles, Jackson and others pointed out many sources of error in the data gathered during the old geodetic surveys that Castle had used to trace the evolution of the bulge.

“For one thing,” Jackson said, “the rods should be calibrated every year. Some were not calibrated for 18 years.”

Another source of error is atmospheric refraction, he said. When someone is sighting through the telescope at a rod, the line of sight can be distorted by variations in atmospheric conditions such as temperature. Although the error is slight, over the course of surveying a line, say, from San Pedro to Saugus to Palmdale, these tiny errors can add up to account for something as big as the Palmdale bulge, Jackson said.

‘People Want to Believe’

“It’s a human issue as well as a scientific issue,” Jackson said. “People want to believe it. . . . There seems to be something in people that likes excitement. When they get some data that’s got some wiggles in it, they blame it on the Earth.”

Castle said that, when the data are adjusted to compensate for these errors, the bulge persists. Jackson and other critics of the bulge are using “the antithesis of the scientific method,” Castle said. “If they can’t explain data, they don’t believe the data,” he said.

A survey of some geologists familiar with the terrain of Southern California--but outside the fray over the bulge--turned up no bulge disbelievers and only a couple who were neutral on the issue. One of the fence-sitters is Bradford Hager, an associate professor of geophysics at Caltech.

“It’s one of those things that’s right on the edge of resolution as to whether it occurred or not,” Hager said. “But if it happened, it would . . . not be totally unexpected.”

“People are just reaching to fantastic lengths to try to discredit this,” said Doug Morton, a USGS geologist based at the University of California, Riverside, who said he is a firm believer.

“I’m not saying you should endorse every new thing that comes along and put your arms around it, but I’ve gone through this thoroughly,” Morton said. “There is all sorts of geological data saying this has been occurring for a long period of time.”

Geodesists Resist Theory

He said that resistance to the theory stems in part from the fact that “geodesists don’t like to deal with a moving Earth.”

“They like to have everything static,” he said. “All of us would be much more comfortable if ‘terra firma’ were as originally enumerated--firm earth. But earthquakes and other changes do happen.”

The section of the San Andreas Fault that twists as it cuts north of Los Angeles in what geologists call the “Big Bend” is “bizarrely complicated . . . a terrible enigma that lots of us have struggled with for years,” Morton said.

There, rather than slipping past each other in a relatively straight line, pieces of the Earth’s crust called the Pacific Plate and the North American Plate butt up against each other. The Palmdale bulge “makes geological sense,” Morton said, and may have been caused by the periodic buildup of stresses along the bend.

Seismic Link Still Questioned

The question of whether such a bulge can be linked to seismic activity is still unresolved, geologists say. The original flurry surrounding the bulge was caused by a widespread feeling that an uplift of such massive proportions might presage an equally massive earthquake, Castle said. A small-scale bulge had been noted before the Sylmar earthquake. Also, the 1905 bulge seemed to be associated with unusual earthquake activity.

But when the recent swelling subsided in 1974, it did so quietly, “singularly free” of any direct link to local seismic activity, Castle said.

The earthquake that shook Palm Springs last week “is near the point of maximum cumulative uplift” of the bulge, said Wayne Thatcher, a USGS geophysicist. But if there is a link, no one knows what it is.

“Certainly there’s an indirect relation,” Thatcher said. “Both are parts of the tectonic activity in the region--mountain building forces.”

Mother Nature’s Message

It is probably a situation where “Mother Nature is trying to tell us something, but we aren’t smart enough to understand it,” said Clarence Allen, a professor of geology and geophysics at Caltech. Allen also said that Jackson has not convinced him that the bulge is an illusion.

More recent surveys of the area, conducted over the past few years by Thatcher and others at USGS, have continued to show dramatic rises and falls of up to six inches in the landscape, Thatcher said. This time, measurements of variations in Earth’s gravity and of changes in horizontal distances are also being taken.

“The more simultaneous things we can measure, the better,” Thatcher said. These measurements are confirming that the region is active, but it is too early to know if the Palmdale bulge is on the rise again, he said.

Laser May Settle Debate

A new technology, employing lasers and satellites, may help put an end to the battle of the Palmdale bulge, according to Caltech’s Hager. A pinpoint beam of laser light is bounced from points on Earth to Defense Department satellites that are part of what is called the Global Positioning Satellite System.

By timing the return of the light reflected back to Earth from four different satellites, the system can determine the distance between two points or the elevation of a point to within a few centimeters, Hager said.

Even with the new technology, the putative Palmdale bulge will not be the last geological phenomenon to generate debate. A dispute has already arisen over the accuracy of some measurements obtained with the satellite system, Hager said. The data seem to show that the speed at which the two sides of the San Andreas Fault slip past each other has dropped over the past four years from six centimeters a year to two or three centimeters a year.

If this is true, he said, it would be another instance where “the Earth doesn’t move in some smooth way” and would make an already complex phenomenon even harder to understand.

The problem is the same as the one that has dogged the century-old technology of geodetic leveling that first measured the Palmdale bulge: Scientists have a habit of “pushing the equipment right up to the edge,” Hager said.