The USGS released a map of excess voltages caused by solar activity. This map was part of a larger report for securing the electrical infrastructure.

Occasionally the sun gives of intense magnetic flares that can cause widespread reactions. This work relies on data acquired by the USGS, Natural Resources Canada and the EarthScope project of the National Science Foundation.

A storm in March 1989 caused a blackout of Quebec, Canada. The great magnetic storm of 1921 caused fires in telegraph stations used by railroad companies

in New York City and other parts of the State. History shows many times when auroras were much more intense showing solar activity can vary considerably.


The new USGS research shows that geologic structure is an important factor affecting storm-induced voltages on the power grid. In particular, the map shows that due to electrically resistive rock, there is high hazard in the northern Midwest and, notably, in the Piedmont formation east of the Appalachian Mountains – an area adjacent to many of the nation’s largest cities.

The map of overvoltage shows if an intense solar flare hit the planet today that widespread damage could cost over $1 trillion to repair.

Already power companies have spark arrestors to cope with lightning etc. Many areas that have thunderstorms have installed a lot of spark arrestors to protect the grid. One bolt of lightning can be several millions of volts and there is a lot of current for a brief period.

A pulse of electromagnetic energy typically comprises many frequencies from very low to some upper limit depending on the source. The range defined as EMP, sometimes referred to as “DC to daylight”, excludes the highest frequencies comprising the optical (infrared, visible, ultraviolet) and ionizing (X and gamma rays) ranges.

Some types of EMP events can leave an optical trail, such as lightning and sparks, but these are side effects of the current flow through the air and are not part of the EMP itself.

A very large EMP event such as a lightning strike is also capable of damaging objects such as trees, buildings and aircraft directly, either through heating effects or the disruptive effects of the very large magnetic field generated by the current. An indirect effect can be electrical fires caused by heating. Most engineered structures and systems require some form of protection against lightning to be designed in.

A home can be protected with some hardware but awareness that damage is possible if lightning is very close. For that reason spare parts are a wise idea. Designing for a nuclear EMP is possible but the cost is high. Protecting the entire electrical infrastructure will likely be very costly.