A geologist prepares for a hurricane, and explains what’s happening

We haven’t even been able to digest the tragedy of Harvey, and now Hurricane Irma is on a collision course for South Carolina. It will not be welcome after our encounters with the floods of Hurricane Joaquim in 2015 and Hurricane Mathew just last year.

Hurricanes derive their energy from the warm waters of the tropical ocean. They hold enormous amounts of moisture that evaporates from the ocean and then condenses, forming clouds that then release the precipitation; this evaporation, condensation and precipitation are a continuous process. Hurricanes also spin at high speeds (counter-clockwise in the Northern hemisphere) and produce high winds. In coastal areas, they induce huge swells of water and coastal flooding. When the hurricane moves over land, and loses its warm water source, the evaporation, condensation and winds decrease, but the precipitation continues until it runs out of atmospheric water.

South Carolina’s coastline is vulnerable to flooding because of the flat topography. The land surface gets saturated with the initial rainfall, and the subsequent rainfall creates overland flow, which results in ponding of the water, leading to flooding. Streets become impassable. Automobiles can be swept away in the floodwaters. Occupants can drown.

In hilly areas or locations with steep gradient, the heavy rainfall washes away everything in its path, from human-made structures to trees, vegetation and soil. All this debris gets deposited in flat areas. It takes days and weeks to clean up the mess, and more work to restore soil where it was lost and plant trees where they were uprooted.

If Hurricane Irma remains on course to pass over South Carolina, coastal evacuation will of course be the No. 1 priority. Between now and then, people living in low-lying areas should check the storm drains around their homes to ensure that they are not clogged with debris so they can carry as much of the water as possible. Outdoor furniture should be secured, and food and water should be stocked at home now — not at the last minute.

And as everyone in Columbia should remember, being 100 miles inland doesn’t necessarily save us from flooding: Anyone near a river or lake should pay close attention to the level of the water, prepare barricades as needed and be prepared to evacuate.

In the past two weeks, we have seen in Texas and Louisiana an even greater magnitude of damage than we had realized a hurricane could cause. The impact on the economy of United States will be felt for months to come. We can only hope that Irma spares us.

This story was originally published September 6, 2017 at 6:02 PM with the headline "A geologist prepares for a hurricane, and explains what’s happening."