The 1900 Galveston hurricane was so deadly primarily due to a combination of factors:

• It was a powerful Category 4 hurricane with sustained winds around 120-140 mph when it struck Galveston, Texas

• The most lethal aspect was a massive storm surge estimated at 15-16 feet that inundated the low-lying island city, which was only about 8 feet above sea level. This surge caused widespread flooding and destructive waves that demolished buildings and drowned thousands

• The city had very little warning because meteorological technology and communication were limited at the time. Wireless ship-to-shore communication and advanced forecasting were not yet available, so residents were largely unaware of the storm's severity and timing

• The construction of buildings was vulnerable to such a storm surge and hurricane-force winds, leading to massive structural failures and debris that caused additional fatalities

• The death toll was enormous, with estimates ranging from 6,000 to 12,000 people, making it the deadliest natural disaster in U.S. history. Approximately 20% of the island's population perished, many drowning or crushed by debris

In summary, the deadly combination of an intense hurricane, a catastrophic storm surge flooding a low-lying city, inadequate warning systems, and vulnerable infrastructure made the 1900 Galveston hurricane extraordinarily lethal