In the Republican response to last night's presidential address to a joint session of Congress, Louisiana Gov. Bobby Jindal chided the lawmakers for earmarking "$140 million for something called volcano monitoring." The funds he was referring to are part of the $787 billion stimulus package signed into law by Pres. Obama earlier this month; some 12 percent ($98.3 billion) of the monies are set aside for transportation and infrastructure projects, including volcano monitoring and other natural disaster prevention programs.

The U.S. Geological Society (USGS) is in charge of keeping tabs on volcanoes in the U.S. and its territories. The agency is currently monitoring more than 150 of them (from Yellowstone in Wyoming to Kilauea in Hawaii), some 65 of which show signs of seismic activity and are more likely than the others to erupt (including Redoubt in Alaska and Mauna Loa in Hawaii). But USGS officials aren't just worried about Hollywood-caliber lava blowups. Other threats include potentially deadly landslides, falling rocky ash, and inundation by toxic gases that can be triggered by volcanic eruptions.

But most active U.S. volcanoes are in remote reaches of Alaska, where few people live and relatively little economic damage stands to occur. So is monitoring volcanoes really necessary?

To find out, we spoke with Ed Venzke, a specialist at the Global Volcanism Program at the Smithsonian National Museum of Natural History in Washington, D.C.

[An edited transcript of the interview follows.]

What is volcano monitoring?
It's exactly what it sounds like. There are a lot of different methods, but it's basically researching exactly what is happening at the volcano. That can include seismic activity, small earthquakes, gas emissions, deformation (bulging of the volcano or sinking), stuff like that.

What can we learn from volcano monitoring?
The main purpose of the monitoring is to learn when new magma is rising in the volcano that could lead to an eruption.

Is it important?
It's extremely important. There are obvious hazards to nearby residents. Beyond human safety, there are huge economic concerns. It's not that eruptions can be stopped, but, like a hurricane, it's good to know when it's coming.

Associated with the monitoring is research of the surrounding area to see where previous lava flows have gone and to see where previous ash fall has occurred. So you get some idea of the history of the volcano and the types of eruptions it typically has. Each volcano is different, so you have to do individual research and individual monitoring.

There's a huge hazard in the air from eruption plumes. Volcanic ash is not like ash from the fireplace. It's basically pulverized rocks and glass particles. Putting glass in a jet engine isn't good. That's why the monitoring in Alaska is extremely important to the aviation industry.

Where are most of the volcanoes?
In the U.S., most of them are in Alaska. Just this summer, there were three erupting at the same time. It's rare that a volcano in Alaska is not erupting. Mount Saint Helens [in Washington State] just recently stopped erupting and Kilauea in Hawaii has ongoing eruptions.

So, they're pretty far from Louisiana?
They are. But there's a volcano down in the Caribbean on Montserrat that's been erupting. There are ash plumes from Alaskan volcanoes that have been tracked all the way to the east coast of the U.S. Some of the plumes from eruptions last summer in Alaska reached as far as Iceland and beyond. You can track the gases from these eruptions around the world. These volcanoes can affect air travel over huge areas.

With airplanes, basically what happens is the glass and ash particles go through the jet engines and are heated up and partially melt and get sticky. As they get part of the way out, they cool and harden in the engine. And if you don't have airflow, the engine stops working. It's not clear how dense a plume you have to go through for this to happen.

What volcanoes should be monitored most closely?
Yellowstone has had huge eruptions in the past, but they're extremely rare events. Certainly in terms of immediate human impact, the biggest worry would be if another one of the Cascade Range volcanoes on the U.S. west coast had another eruption. The worst scenario would be if Mount Saint Helens had another eruption of the size it did in 1980 [which killed 57 people and caused an estimated $1.1 billion in damage]—or Mount Rainier near Seattle or Mount Hood near Portland, Oregon. Those are more likely to erupt sooner than Yellowstone. It's great to talk about Alaska, but there aren't a lot of people there. It's a big aviation hazard, but if a volcano [blows] on the west coast, there would be a much greater human impact.

Can you name an instance when volcano monitoring has paid off?

Mount Saint Helens was a great example. The ideal example was not in the U.S., rather it was in the Philippines from Mount Pinatubo in 1991. The USGS's Volcano Disaster Assistance Program (VDAP) responded to that. From the U.S. Navy base there, VDAP officials went in at the first sign of activity and installed a lot of monitoring equipment and did quick emergency research.

Are there any natural disasters the government doesn't monitor?
I can't think about any offhand. There are earthquakes and volcanoes as well as floods, tornadoes, hurricanes—all the weather events. You know, compared to flooding, volcanic eruptions don't impact as many people on an annual basis, but they're dramatic events and can certainly have huge human and environmental impacts when they do come. And it's good to know when one's coming!