After a surreal week in Texas, it’s clear we need to expect the unexpected when it comes to our infrastructure as extreme weather events – from wildfires to hurricanes – intensify.

Last week a combination of unprecedented cold, wintry weather and rolling blackouts crippled Texas. Several days of freezing weather and power outages led to 70 deaths and counting across the region. The lasting fallout includes clean up from all the burst pipes and other issues that may rival Hurricane Harvey’s price tag.

So what happened?

First, a shaky polar vortex (which some scientists blame on climate change) brought a record-breaking deep freeze to Texas.

Then, several factors contributed to a failure of Texas’s grid:

• The cold that made households ratchet up the thermostat also caused mechanical failures in unweatherized equipment. Some wind turbines and nuclear plants had issues, yes, but the biggest culprits were crippled natural gas wellheads and processing plants. At one point, 30 gigawatts— or nearly half the state’s natural gas capacity— went offline as demand for electricity and heat soared.

• Texas’s unique electricity market – ERCOT – operates as an “energy-only” market where customers only pay for energy generated. Others use “capacity markets”— essentially paying for more generation than is needed – as insurance for huge demand events like the deep freeze.