Steve Cotler

Steve Cotler

Enhanced Geothermal Energy and Man-Made Earthquakes

Drill down just a few miles into the earth’s crust, and the temperature will rise substantially. This heat comes from three sources: emissions from radioactive minerals, the compressive force of gravity, and to a lesser extent, solar energy absorbed at the earth’s surface. Although such energy is not truly renewable (radioactive elements do eventually decay to energy-flat states), within any reasonable estimate of mankind’s tenancy on this planet, geothermal power is essentially limitless.

There are several techniques for transducing this energy from underground heat to in-the-grid electricity. One of these, a technology called Enhanced Geothermal Systems (EGS), is currently being tested by Sausalito-based AltaRock Energy only 12 beeline miles from my home in Northern California. One would think this would be big news in Wine Country, but except for a 2008 mention of seed funding by and several high-profile venture capital firms, this potentially earth-shaking (remember that adjective!) demonstration project has gone unmentioned in my local paper, the Santa Rosa Press Democrat. But on June 23, 2009, NYT journalist James Glanz wrote a long article suggesting that AltaRock’s EGS experiment might cause earthquakes. It was reprinted four days later in the New York Times-owned Press Democrat along with a side story about earthquakes in Anderson Springs, the tiny Lake County hamlet closest to the drilling site.

Glanz based his warning on a 2006 earthquake caused by an EGS project in Basel, Switzerland, but he did not go unchallenged. Green Momentum, a specialized media company that focuses on providing independent news coverage events and developments affecting the “cleantech” industry, immediately opined that Glanz’s article “was certainly alarmist, if not genuinely alarming.

As a survivor of the eight-year Bush/Cheney “cone of silence,” I am suspicious of PR Kool-Aid, but given the publicly available information about EGS in both Switzerland and California, it appears that there are many differences between the EGS processes tested by Geothermal Explorers International. Ltd. in Basel and the AltaRock test just underway near Anderson Springs.

Geothermal energy has great potential for helping to solve our long-term energy problem. Producing energy from geothermal sources is mostly clean (geothermal sources do tend to release greenhouse gases trapped deep within the earth, but these emissions are usually much smaller than those of fossil fuels) and power plants can be situated almost anywhere. The heat is onmipresent…just below the top layer of the crust. MIT chemical engineering professor Jefferson Tester calculates that the US’s total annual energy consumption is 100 exajoules. It doesn’t matter if that number is incomprehensible. Prof. Tester estimates that the geothermal resource for the whole country is about 14,000,000 exajoules. In oilman talk, that’s a lot of reserves.

Luther Burbank, early geothermal investor
             Luther Burbank          early geothermal investor

Healdsburg, the Sonoma County town in which I live, gets 43% of its electricity from geothermal sources (Q3 2009 report), almost entirely from The Geysers, the most productive geothermal energy site in the United States. The Geysers Development Company began selling electricity to Healdsburg in 1926 (world-renown botanist/horticulturalist Luther Burbank, a Sonoma County transplant, was one of the original investors), but as oil came down rapidly in price in the mid 30s, energy generation at The Geysers ceased to be profitable, and operations ceased. The first modern plant went online in 1960, with generation peaking in the ’80s at about 1,500 megawatts, enough energy to power about 1.5 million homes. Because this high level of production began to diminish available underground heat at The Geysers, output was purposely decreased to about 800 megawatts in order to stretch the site’s useful life.

Each day, Calpine Energy and the state-run Northern California Power Agency pump 11 million gallons of treated wastewater through a 41-mile underground pipeline from Sonoma County seat Santa Rosa and inject it into the extremely hot, permeable rock below. The water boils, creating high pressure steam that rises to the surface where it turns turbine generators, producing enough electricity to power most of the North Bay.

Geology of The Geysers

The geology of The Geysers is special. The caprock there is thinner than average, and the sub-surface rock is riddled with cracks, making the water-to-steam process relatively straightforward. AltaRock’s EGS technology, however, does not require fissured rock. This is an advantage: there are many, many more sites that sit above hot, solid rock than above hot, fractured rock. At Anderson Springs—which is near, but not in The Geysers field—AltaRock will drill deeply and inject water at very high pressure, thus cracking the extremely hot, solid rock, and producing electricity with the resultant steam. When the steam condenses, the water will be reinjected into the hot rocks below.

So what is the New York Times article worried about?

In 2001, Geothermal Explorers, a Swiss company, undertook an EGS project dubbed Deep Heat Mining Basel. In December 2006, at a depth of just over 5,000 meters (3.1 miles), full-scale injection of water triggered a 3.4 magnitude earthquake, big enough to rattle both the local windows and its citizenry. Geothermal Explorers immediately and voluntarily shut the project down. Glanz’s report suggests that the AltaRock experiment could engender similar man-made temblors in Lake County.

Anderson Springs knows about earthquakes. The number of earthquakes with magnitude greater than 2.0 has increased dramatically over the last several decades. (See chart below.) Not surprisingly, some residents have mobilized, forming the Anderson Springs Community Alliance. Its mission is to raise “public awareness about numerous significant environmental impacts affecting the community due to ongoing geothermal development.”

AltaRock gave a detailed response to Glanz’s article on its website:

• We took extraordinary care in choosing our site at the Geysers to avoid siting on a major fault. The Basel Project drilled into a significant fault.
• Smaller faults mean smaller events, and the faults in the Geysers area are significantly smaller than at Basel.
• The geology of the Geysers is very different – seismic studies predict events at the Geysers likely to be imperceptible at the surface.
• Events of similar magnitude to Basel occur frequently in California.
• Basel produced an event with a magnitude which is more than 10 times the size of the maximum event estimated for our project..
• We have installed monitoring and control procedures and designed pressure relief mechanisms to minimize any impact.
• We are employing proprietary technologies to ensure a safe and well-controlled project.
• We have actively involved and informed the community.

Getting energy from geothermal sources is important…and controversial. Is it worth the risk of more earthquakes? Is the risk real?

There will be more in subsequent posts.


  1. […] described in a previous post, Sausalito-based AltaRock Energy is drilling a Lake County test well aimed at producing energy by […]

  2. […] previous posts (Part 1 and Part 2) described the EGS project that AltaRock had undertaken in The Geysers, a geologically […]

  3. […] previous posts (Part 1 and Part 2) described the EGS project that AltaRock had undertaken in The Geysers, a geologically […]

  4. Jane says:

    thank you for the very informative and quite interesting article. You know the best way to hide something (man made earthquakes) is to keep it in plain sight!! Most people do not ‘want’ to believe that we can create earthquakes on purpose.

  5. Your comments on EGS are pretty right-on except that I believe the side effects of EGS are manageable after we get more experience with them. In the meanwhile, I hope that the demonstration projects will all be sited where there are few homes around.

    As I understand it, the AltaRock project was actually shut down because they broke too many drill bits. While they were shut down, they analyzed the prospects for earthquakes and discussed with all the concerned parties and decided to abandon the project entirely. They seem to be much better citizens than the oil companies. AltaRock have started up at another site now. See

    I think that many of the earthquakes that are noticeable off-site are due to pushing the injection too hard. Of course, as is the case with any commercial enterprise, the management wants to maximize immediate profit, so they push everything. In fact, I read one article that showed that a conventional geothermal plant at The Geysers is being pushed so hard that the reservoir temperature is steadily declining with no sign of leveling off. It reminds me of what sometimes happens in developing oil fields. The operator pushes his production to the point that water invades the reservoir and dilutes oil production or even stops it. Slower production allows the oil/water interface to equilibrate and avoids the problem until the reservoir is more nearly emptied. Some people never learn!

    I think that when rules for producing EGS are better learned and regulations and tax policy favor long-term productivity over short term, this over-injection will diminish. Also by using pulsed fracturing and injection in connection with better fracture monitoring, higher injection rates might be achieved without noticeable earthquakes.

    A really neat technology to improve and reduce the cost of drilling deep wells in hard rock is being developed by Bob Potter et al. Potter actually invented EGS while working at Los Alamos in the 1970s. See for details.

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