Nepal was devastated by a magnitude 7.8 earthquake on Saturday, which originated outside the capital Kathmandu and has been followed by a series of powerful aftershocks. More than 4,000 people have been killed by the disaster.

Saturday's quake was many times more powerful than the 7.0 quake that ruined Haiti in 2010. Nepal's worst recorded earthquake in 1934 measured 8.0 and all but destroyed much of the country's large cities.

CBS News science contributor Michio Kaku, a physics professor at the City College of New York, told "CBS This Morning" that scientists have been able to study earthquake data going back 100 years, and have observed that there is frequently an interval of 80 years between big earthquakes.

Asia's plate tectonics help explain why that's so.

"It turns out that India and China are colliding," Kaku said. "And the collision of the two created the Himalayan Mountains, the buckling effect, and the two are increasing at a known rate, at around two inches per year. That's the rate at which your fingernails grow. Now that's not very much, but spread out over a thousand miles and propelled by a subcontinent, we're talking about an enormous amount of energy that's regularly plowing into each other."

Kaku said the biggest concern now, however, is the likely health crisis that will follow the tremors.

"We are talking about a million homeless people without sanitation and without medical care, sealed off from the rest of the world," Kaku said.

Diseases like cholera can flourish in the unsafe conditions, he said.

Another major concern is the shaking that follows the initial earthquake.

"The aftershocks could go on not just for a few hours or days, but for weeks," Kaku said. "And so people don't want to go back into their houses because they are so flimsy. They collapse like a house of cards. Even the aftershocks are collapsing buildings there."

The devastating consequences are due to the fact that this was a "shallow quake," Kaku said, which took place just five miles beneath the surface and packed about 10 hydrogen bombs' worth of energy.

"If it was much deeper into the earth, the effect of it would have been minimal, but because it was so close to the surface of the earth, people got the brunt of the shaking," Kaku said. "The city of Kathmandu shifted 10 feet -- an entire city was shifted by the force of this earthquake."

In addition to crumbling cities and towns, the earthquake also affected Nepal's most famous peak, Mt. Everest, where more than a dozen climbers were killed by an avalanche that the shaking triggered. Even though avalanches can be hard to predict, there was a warning about the possibility of one there last week.

"People get overconfident thinking that they know these things, they are seasoned climbers, but these are unpredictable," Kaku said.