A pyroclastic flow (also known scientifically as a pyroclastic density current) is a fast-moving current of hot gas and rock (collectively known as tephra), which reaches speeds moving away from a volcano of up to 700 km/h (450 mph).The gas can reach temperatures of about 1,000 Â°C (1,830 Â°F).Pyroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope.They are a common and devastating result of certain explosive volcanic eruptions.yroclastic flows normally hug the ground and travel downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope.
Optimal Reading. An optimal reading is considered anything lower than 120/80. The actual number of 120/80 is not considered perfect--but actually numbers lower are considered to be optimal. For example, someone with a blood pressure reading of 116/76 has an optimal reading.ptimal Reading. An optimal reading is considered anything lower than 120/80. The actual number of 120/80 is not considered perfect--but actually numbers lower are considered to be optimal. For example, someone with a blood pressure reading of 116/76 has an optimal reading.
View All. For a long time, normal blood pressure was defined as 120/80 mm Hg (systolic/diastolic). Recently, however, the American Heart Association revised its guidelines about what an optimal blood pressure range is, and when blood pressure is considered too high or too low. While 120/80 used to be considered normal, the new guidelines define three levels of abnormal blood pressure values. 120-139 / 80-89 is now considered to be âprehypertensionâ (or âalmost high blood pressure), and doctors are watching blood pressures in this range more carefully than in the past.