Weather Watch

Why Death Valley is littered with Mylar balloons

PG&E supervisors Matt Jones holding Mylar metallic balloons.
PG&E supervisors Matt Jones holding Mylar metallic balloons.

Almost every day, Ranger Jay Snow retrieves Mylar balloons from Death Valley National Park. At 282 feet below sea level, it is the lowest point in the United States. It’s also the hottest; the valley reached a record 134 degrees on July 10, 1913. This park is a land of fierce beauty with magnificent land forms surrounded by snowcapped mountains.

“You hike for miles through this vast wilderness area and discover a canyon, a canyon that only a few people have probably walked before, but like clockwork you come across one of these stinking metallic balloons,” Snow said.

One of his fellow rangers has found so many of these colorful chrome-like spheres with “Happy Birthday” written in joyful letters along the top that he wallpapers the inside of his cabin with them.

Two types of balloons are in use today: Mylar and latex. Mylar balloons are made with Mylar nylon, a material not classified as biodegradable. They often are coated with a metallic finish that conducts electricity.

On the other hand, latex balloons are elastic and are composed of natural rubber that is biodegradable. Latex weather balloons, the kind launched from Vandenberg Air Force Base, are filled with helium and are about 4 feet in diameter at sea level. These balloons rise through the atmosphere and expand in diameter.

By the time they reach about 100,000 feet, they expand to about 40 feet in diameter. Air temperatures at this altitude can drop to minus-50 degrees or lower and freeze the latex. At this high altitude, a frozen balloon undergoes “brittle fracturing” and ruptures into small shreds of rubber that then fall to earth.

However, Mylar balloons do not go higher than about 3,000 feet to 7,000 feet before they either explode or lose their “lift.” This is because of their inability to expand to any great extent.

This fact is key to understanding how so many Mylar balloon find their way to Death Valley. You see, for most of the year the winds blow from the Pacific Ocean over Los Angeles toward the east at elevations typically below 6,000 feet. These “onshore” winds carry Mylar balloons that have broken free or have been released from the greater Los Angeles area, and find themselves on a journey toward Death Valley National Park.

Easterly (offshore) winds are predominant at late fall and winter and may be transporting these balloons from the Las Vegas area. In both of these scenarios, the winds that are carrying these balloons hit the windward slopes of mountains that surround most of Death Valley and quickly rise. The balloons are lifted to their bursting point and fall to the valley floor.

Not only do these metallic balloons litter pristine wilderness areas, but they also are a major cause of power outages. When these metallic balloons come in contact with electric power lines, they often cause outages. When metallic balloons get tangled in power lines, it has the same effect as if a wrench came in contact with both the negative and positive terminals of a car battery. It can cause power lines to short out, which can trigger the conductor to break, resulting in energized lines falling to the ground.

Last year, metallic balloons that drifted into PG&E power lines caused nearly 300 outages and affected electric service to nearly 165,000 homes and businesses throughout Northern and Central California.

To reduce this number and to help ensure that everyone can enjoy Father’s Day safely today, PG&E reminds customers to follow these important safety tips for metallic balloons: