Flow rates in the axial hot springs of the East Pacific Rise (21°N): Implications for the heat budget and the formation of massive sulfide deposits

The first in-situ measurements of flow rates in submarine hot springs (temperatures between 275° and 350°C) were made in the hot springs of the East Pacific Rise at 21°N during November, 1981. The flow rates ranged between 0.7 and 2.4 m/s. We estimate that the total rates at which heat and mass are transported from the three hot spring areas—OBS, National Geographic, and Southwest Vents—are ca. 2.2×10⁸ W and 150 kg of fluid/s respectively. The very high rate of heat loss precludes the existence of hot springs as steady state features of the East Pacific Rise at 21°N. We estimate that hot springs are active for a maximum of ca. 40,000 years. Chemical and/or mechanical clogging of the vents can drastically reduce the lifetime of the hot springs.Using a simple model of plume development 1], we calculated that less than 3% of the sulfide particles that are entrained in the hydrothermal plumes at 21°N settle from the plumes before dispersal by a lateral submarine current at a height of ca. 250 m above the seafloor 2]. The time that is required to form the sulfide mounds that surround the hot springs by the accumulation of sulfide particles that settle from the plumes is ca. 70–85 years. The current rate at which sulfide particles settle from the hydrothermal plumes and accumulate near the hot springs appears to be too small to lead to the formation of large massive sulfide deposits such as the Mavrouni deposit on Cyprus 3], within the time limits that are suggested by our thermal energy balance calculations.