Rich Pedroncelli / AP

Robin and Scott Spivey walk past the wreckage of their Tudor-style dream home on Monday. They had to abandon it when the ground gave way causing it to drop 10 feet below the street in Lakeport, Calif. Officials believe that water that has bubbled to the surface is playing a role in the collapse of the hillside subdivision, forcing the evacuation of eight homes and endangering another 10.

LAKEPORT, Calif. -- Scott and Robin Spivey had a sinking feeling that something was wrong with their home when cracks began snaking across their walls in March.

The cracks soon turned into gaping fractures, and within two weeks their 600-square-foot garage broke from the house and the entire property — manicured lawn and all — dropped 10 feet below the street.

It wasn't long before the houses on both sides collapsed as the ground gave way in the Spivey's neighborhood in Lake County, about 100 miles north of San Francisco.

"We want to know what is going on here," said Scott Spivey, a former city building inspector who lived in his four-bedroom, Tudor-style dream home for 11 years.

Eight homes are now abandoned and 10 more are under notice of imminent evacuation as a hilltop with sweeping vistas of Clear Lake and the Mount Konocti volcano swallows the subdivision built 30 years ago.

The situation has become so bad that mail delivery was ended to keep carriers out of danger.

"It's a slow-motion disaster," said Randall Fitzgerald, a writer who bought his home in the Lakeside Heights project a year ago.

Unlike sinkholes of Florida that can gobble homes in an instant, this collapse in hilly volcanic country can move many feet on one day and just a fraction of an inch the next.

Officials believe water that has bubbled to the surface is playing a role in the destruction. But nobody can explain why suddenly there is plentiful water atop the hill in a county with groundwater shortages.

Rich Pedroncelli / AP

Jagtar Singh gazes from the doorway of one of the bedrooms that collapsed as the ground gave way beneath his home in Lakeport, Calif.

"That's the big question," said Scott De Leon, county public works director. "We have a dormant volcano, and I'm certain a lot of things that happen here (in Lake County) are a result of that, but we don't know about this."

Other development on similar soil in the county is stable, county officials said.

While some of the subdivision movement is occurring on shallow fill, De Leon said a geologist has warned that the ground could be compromised down to bedrock 25 feet below and that cracks recently appeared in roads well beyond the fill.

"Considering this is a low rainfall year and the fact it's letting go now after all of these years, and the magnitude that it's letting go, well it's pretty monumental," De Leon said.

County officials have inspected the original plans for the project and say it was developed by a reputable engineering firm then signed off on by the public works director at the time.

"I can only presume that they were checked prior to approval," De Leon said.

The sinkage has prompted county crews to redirect the subdivision's sewage 300 feet through an overland pipe as manholes in the 10-acre development collapsed.

Consultant Tom Ruppenthal found two small leaks in the county water system that he said weren't big enough to account for the amount of water that is flowing along infrastructure pipes and underground fissures, but they could be contributing to another source.

"It's very common for groundwater to shift its course," said Ruppenthal of Utility Services Associates in Seattle. "I think the groundwater has shifted."

If the county can't get the water and sewer service stabilized, De Leon said all 30 houses in the subdivision will have to be abandoned.

The owners of six damaged homes said they need help from the government.

The Lake County Board of Supervisors asked Gov. Jerry Brown to declare an emergency so funding might be available to stabilize utilities and determine the cause of the collapse. On May 6, state Sen. Noreen Evans, D-Santa Rosa, wrote a letter of support asking Brown for immediate action. The California Emergency Management Agency said Brown was still assessing the situation.

On Wednesday, the state sent a water resources engineer and a geologist to look at the problem. Sen. Dianne Feinstein sent a representative the next day.

Lake County, with farms, wineries and several Indian casinos, was shaped by earthquake fault movement and volcanic explosions that helped create the Coast Ranges of California. Clear Lake, popular for boating and fishing, is the largest fresh water lake wholly located in the state.

It is not unusual for groundwater in the region to make its way to the surface then subside. Many natural hot springs and geysers receded underground in the early 1900s and have since been tapped for geothermal power.

Homeowners now wonder whether fissures have opened below their hilltop, allowing water to seep to the surface. But they're so perplexed they also talk about the land being haunted and are considering asking the local Native American tribe if the hilltop was an ancient graveyard.

"Someone said it must be hexed," said Blanka Doren, a 72-year-old German immigrant who poured her life savings into the house she bought in 1999 so she could live on the rental income.

The home shares a wall with her neighbor, Jagtar Singh — who had two days of notice to move his wife, 4-year-old daughter and his parents before the hill behind the back of his home collapsed — taking the underside of his house and leaving the carpet dangling.

Doren is afraid that as Singh's house falls it will take hers with it. Already cracks have spread across her floors.

Damaged houses in the subdivision have been tagged for mandatory removal, but the hillside is so unstable it can't support the heavy equipment necessary to perform the job.

"This was our first home," said Singh, who noticed a problem in April when he could see light between the wall and floor of his bedroom. A geotechnical company offered no solutions.

"We didn't know it would be that major, but in one week we were gone," he said.

So far insurance companies have left the owners of the homes — valued between $200,000 and $250,000, or twice the median price in the county — dangling too. Subsidence is not covered, homeowners said. So until someone figures out whether something else is going on, they'll be in limbo.

"It's a tragedy, really," contractor Dean Pick said as he took photos for an insurance company. "I've never seen anything like it. At least that didn't have the Pacific Ocean eating away at it." 

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Al-Qaida remains a threat, but intense U.S.-led pressure is working and could relegate it and similar organizations to having only "symbolic importance," the nation's intelligence chief said Tuesday.

When and if that happens, the U.S. will no longer have the luxury of focusing on one dominant threat, James R. Clapper, the director of national intelligence, told senators in the intelligence community's annual assessment of threats to national security.

Rather, the "multiplicity and interconnectedness of potential threats, and the actors behind them, "will combine into an amorphous but critical challenge," Clapper said in testimony before the Senate Intelligence Committee. He was joined at the hearing by CIA Director David Petraeus. 

While people find it easier to identify a single target — like the Soviet Union during the Cold War or al-Qaida during President George W. Bush's war on terrorism — "it is virtually impossible to rank, in terms of long-term importance, the numerous potential threats to U.S. national security," he said.

Clapper warned that security challenges today cut across political, economic, military and transnational trends. They reflect a "quickly changing international environment" that includes new political and military developments, the rise of "nonstate actors" — like regional terror and paramilitary groups — and ever-increasing access by individuals to deadly technologies.  

The good news, he said, is that the resistance to al-Qaida over the past decade has established that sustained pressure works.

"The intelligence community sees the next two or three years as a critical transition phase for the terrorist threat, particularly for al-Qaida and like-minded groups," he said. "... As long as we sustain the pressure on it, we judge that core al-Qaida will be of largely symbolic importance to the global jihadist movement."

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Clapper, a retired Air Force general and former head of the Defense Intelligence Agency, was confirmed as national intelligence director in August 2010. 

In his testimony Tuesday, Clapper and Petraeus talked in detail about al-Qaida and other threats to national security:

• Al-Qaida: The death of Osama bin Laden deprived radical Islam of it "most iconic and inspirational leader" at a time when its capabilities had already been degraded by years of U.S.-led pressure, Clapper said. Al-Qaida's new leader, Ayman al-Zawahiri, is unlikely to change the organization's strategic direction, even though "most al-Qaida members find Zawahiri's leadership style less compelling than bin Laden's image as a holy man and warrior" and "will not offer him the deference they gave bin Laden." 

As a result, "al-Qaida increasingly will seek to execute smaller, simpler plots to demonstrate relevance to the global jihad," Clapper said. In fact, smaller regional groups like al-Qaida in the Arabian Peninsula and al-Qaida in Iraq are likely to "surpass the remnants of core al-Qaida in Pakistan" as threats to U.S. interests. 

• Syria: It's only a matter of time before Syrian President Bashar Assad falls from power, Clapper said, but it could be a long time because of intervention by Iran and the militant Islamist group Hezbollah and military supplies from North Korea. That makes it difficult for the West to plan for "a post-Assad situation," he said.
• Weapons of mass destruction: The spread of biological, chemical and  nuclear weapons is "among our top concerns," Clapper said, because "the time when only a few states had access to the most dangerous technologies is past."

Biological and chemical materials "move easily in our globalized economy, as do the personnel with scientific expertise to design and use them," he said. 

Open Channel: Israeli Embassy, US tourists among likely targets of bomb plot

While no recognized countries are yet known to have provided direct WMD assistance to terrorist groups, that could change: "As governments become unstable and transform, WMD-related materials may become vulnerable to nonstate actors, if the security that protects them erodes," he said.

• Iran: Petraeus said he believed the International Atomic Energy Agency's report in November — which said Iran is on the verge of a nuclear "breakthrough" that could allow it to launch a missile able to hit Israel and Europe — is accurate.  

But Iran's willingness to allow IAEA inspectors to extend their stay in Tehran this week indicates that new sanctions on Iran's central bank are beginning to bite. (NBC News has reported that China, Iran's biggest oil customer, has recently reduced its purchases of Iranian oil after behind-the-scenes negotiations with U.S.)

Msnbc.com: Will Iran make good on its threat against US?

• North Korea: The death of supreme leader Kim Jong-il is unlikely to lead to any fundamental change in Pyongyang's isolation and belligerence, Petraeus said. There's no reason to believe, he warned that the new leader, Kim Jong-un, will stop the country's exports of ballistic missiles and other materials to Iran, Syria and possibly other countries.

• Cyber-threats: Advances in information technology have opened the door to mass-scale collection of personal and governmental data by China, Russia and numerous independent groups, Clapper said.

Unfortunately, "innovation in functionality is outpacing innovation in security, and neither the public nor private sector has been successful at fully implementing existing best practices," he said. That's shown by well-publicized intrusions into the NASDAQ computer system and International Monetary Fund networks, underscoring the "vulnerability" of the U.S. economy.

• Health threats and natural disasters: Clapper pointed to the earthquake and tsunami in Japan as an example of what could go wrong even when a government acts appropriately.  

"Although Tokyo responded adequately in the immediate aftermath of Japan's largest earthquake, the triple disaster contributed to Prime Minister (Naoto) Kan's resignation," he said. Beyond the immediate health and safety concerns, such developments open the way for militant groups to "challenge and potentially destabilize governments" that never would have been considered vulnerable, he said.

"Although we can say with near certainty that new outbreaks of disease and catastrophic natural disasters will occur during the next several years, we cannot predict their timing, locations, causes or severity," he warned.

Andrea Mitchell and Courtney Kube of NBC News contributed to this report from Washington.

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