Geography
Two Holocene calderas are found at Raoul. The older caldera cuts the center of Raoul Island is about 2.5 km × 3.5 km (1.6 mi × 2.2 mi) long x wide. Denham caldera, formed during a major dacitic explosive eruption about 2200 years ago, truncated the western side of the island and is 6.5 km × 4 km (4.0 mi × 2.5 mi) long x wide. Its long axis is parallel to the tectonic fabric of the Havre Trough that lies west of the volcanic arc. Historical eruptions at Raoul during the 19th and 20th centuries have sometimes occurred simultaneously from both calderas, and have consisted of small-to-moderate phreatic eruptions, some of which formed ephemeral islands in Denham caldera. A 240 m (787 ft) high unnamed submarine cone, one of several located along a fissure on the lower NNE flank of Raoul volcano, has also erupted during historical time, and satellitic vents at Raoul are concentrated along two parallel NNE-trending lineaments. The Denham caldera was named for the nearby Denham Bay, itself named by Capt M H Denham in HMS Herald who came to complete a (chart) survey of the island on July 2, 1854. His son Fleetwood James Denham (16yrs) died from a tropical fever, and was buried near the beach at the head of Denham Bay, where a number of the grass-grown graves of former settlers were. The brass plaque heading this grave has been preserved.
Three small lakes, Blue Lake (1.17 km2/0.45 sq mi, about 40% overgrown), Green Lake (160,000 m2/1,700,000 sq ft) and Tui Lake (5,000 m2/54,000 sq ft, drinking water quality) are located in the northern caldera of Raoul Island. The plains surrounding the lakes are called Pumice Flats.
Raoul Island has a humid subtropical climate with warm, wet weather throughout the year.
| Climate data for Raoul Island | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| Average high °C (°F) | 25.0 (77.0) |
25.7 (78.3) |
24.9 (76.8) |
23.6 (74.5) |
21.7 (71.1) |
20.1 (68.2) |
19.1 (66.4) |
19.0 (66.2) |
19.6 (67.3) |
20.5 (68.9) |
22.0 (71.6) |
23.6 (74.5) |
22.1 (71.8) |
| Average low °C (°F) | 19.7 (67.5) |
20.5 (68.9) |
19.9 (67.8) |
18.3 (64.9) |
16.4 (61.5) |
14.8 (58.6) |
13.7 (56.7) |
13.3 (55.9) |
14.0 (57.2) |
14.9 (58.8) |
16.4 (61.5) |
18.2 (64.8) |
16.7 (62.1) |
| Precipitation mm (inches) | 128 (5.04) |
153 (6.02) |
162 (6.38) |
102 (4.02) |
129 (5.08) |
171 (6.73) |
150 (5.91) |
132 (5.2) |
110 (4.33) |
86 (3.39) |
94 (3.7) |
141 (5.55) |
1,558 (61.34) |
| Source: NIWA National Climate Database | |||||||||||||
Read more about this topic: Raoul Island
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