25 June 2004

African dust falls on Florida and Texas

Forrest M. Mims III

Africa visited Florida and Texas last week. The sky last Thursday evening was strangely tinted with its dust.

The dust that arrived in South Texas on Thursday evening continued through the weekend. The height of the event occurred Friday and Saturday. Some was still present on Sunday and Monday.

The dust could be seen on weather radars. it formed a huge, bright disk around the Sun. Before sunset, it formed a dark band over the horizon.

While this was a major dust event, it was by no means the biggest we have experienced. If you measure these transoceanic dust storms by the dust on the windshield of your car, it was fairly minor. Several years ago so much Sahara dust arrived during one event that entire cars were coated with it.

The Sahara and Gobi Deserts are among the world's largest. Every year windstorms whip sand and dust up to 10,000 feet or even higher.

In early spring, Asian dust blows across the Pacific Ocean to North America. During late spring and summer, Sahara dust storms move from South America and Europe and direct their winds toward North America.

It's difficult to imagine the size of these dust storms.
On some days last April, dust from China covered most of the Pacific Ocean north of Hawaii.

African dust forms massive clouds over the Atlantic Ocean and the Mediterranean Sea. The clouds can be the size of Spain or larger.

For centuries these dust clouds have provided iron to plants growing in Central and South American rain forests.

So much Sahara dust blows over the Atlantic that the bottom of portions of that ocean are paved with the stuff. Much of the soil in Bermuda is composed of African dust.

Asian and African wind storms have been happening for so long that the dust they blow across much of the United States is intermingled with our native soil. So are other less desirable ingredients that accompany the dust, including pesticides, heavy metals, mold spores, bacteria and even animal waste.

Residents of the Caribbean know about this all too well, for many of them suffer from asthma directly related to dust from Africa.
Three years ago our daughter Sarah collected and identified Sahara dust. She did this for a science fair project.

This inspired me to collect some Sahara dust on Friday. The first thing I saw while examining the specimen through a microscope was a fungus spore! While it's not possible to say if it sailed all the way from Africa, Florida scientists have found plenty of spores and bacteria in Sahara dust.

Forrest M. Mims III and his science are featured online at http://www.forrestmims.org/.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.