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.
Now a blood pressure of 120/80 is considered normal, and blood pressure readings of 130â139 are considered pre-hypertension. Readings above 140/90 are considered high blood pressure, and the current thinking is that anyone falling into this category should be taking medication to lower blood pressure.urrently the textbook definition of normal blood pressure is 120/80 mmHg. But the definition of normal has changed over the years. At one time, it was believed that normal systolic blood pressure was 100 plus your age. In the 1970s, intervention wasn't even recommended until pressures exceeded 165/95.